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2.1: Chapter 2 - What Is a Search? The Basics

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    With the readings for this chapter, we begin our exploration of the Fourth Amendment to the Constitution of the United States. The Fourth Amendment is short, just 54 words, and it reflects the desires of those who wrote and ratified it to protect Americans against unreasonable government intrusion into their lives. The Amendment mentions some of the more important aspects of a person’s life—her house, her papers, her effects, even her “person,” that is, her body—and declares that government agents may not unreasonably search or seize those things. Here is the text:

    “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no warrants shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”

    These words have inspired arguments about their meanings. For example, what counts as a “house” and thereby merits protection from unreasonable searches? Is it limited to physical buildings in which people live, or is some area outside the structure included? We will see later that the Court eventually defined the concept of “curtilage,” which is an outdoor area that the Court treats as part of the “house.”

    Over the coming weeks, students will encounter vigorous debate over the meaning of “reasonable.” When is it reasonable for a police officer to stop and frisk a pedestrian about whom the officer has suspicion? When is it reasonable for police to search cars without warrants? For now, we will set aside the concept of reasonableness for one simple reason: Before something can be an “unreasonable search,” it must first be a “search.” The cases assigned for this chapter concern the definition of “search” for purposes of Fourth Amendment jurisprudence. (Similarly, before something can be an “unreasonable seizure,” it must first be a “seizure.” We will consider the definition of “seizure” later in the semester.)

    In the first case, Katz v. United States, the Justices attempt to bring their definition of “search” into the modern world.

    Supreme Court of the United States

    Charles Katz v. United States

    Decided Dec. 18, 1967—389 U.S. 347

    MR. JUSTICE STEWART delivered the opinion of the Court.

    The petitioner was convicted in the District Court for the Southern District of California under an eight-count indictment charging him with transmitting wagering information by telephone from Los Angeles to Miami and Boston in violation of a federal statute. At trial the Government was permitted, over the petitioner’s objection, to introduce evidence of the petitioner’s end of telephone conversations, overheard by FBI agents who had attached an electronic listening and recording device to the outside of the public telephone booth from which he had placed his calls. In affirming his conviction, the Court of Appeals rejected the contention that the recordings had been obtained in violation of the Fourth Amendment, because “[t]here was no physical entrance into the area occupied by [the petitioner].” We granted certiorari in order to consider the constitutional questions thus presented.

    The petitioner had phrased those questions as follows:

    “A. Whether a public telephone booth is a constitutionally protected area so that evidence obtained by attaching an electronic listening recording device to the top of such a booth is obtained in violation of the right to privacy of the user of the booth.

    “B. Whether physical penetration of a constitutionally protected area is necessary before a search and seizure can be said to be violative of the Fourth Amendment to the United States Constitution.”

    We decline to adopt this formulation of the issues. In the first place, the correct solution of Fourth Amendment problems is not necessarily promoted by incantation of the phrase “constitutionally protected area.” Secondly, the Fourth Amendment cannot be translated into a general constitutional “right to privacy.” That Amendment protects individual privacy against certain kinds of governmental intrusion, but its protections go further, and often have nothing to do with privacy at all. Other provisions of the Constitution protect personal privacy from other forms of governmental invasion. But the protection of a person’s general right to privacy—his right to be let alone by other people—is, like the protection of his property and of his very life, left largely to the law of the individual States.

    Because of the misleading way the issues have been formulated, the parties have attached great significance to the characterization of the telephone booth from which the petitioner placed his calls. The petitioner has strenuously argued that the booth was a “constitutionally protected area.” The Government has maintained with equal vigor that it was not. But this effort to decide whether or not a given “area,” viewed in the abstract, is “constitutionally protected” deflects attention from the problem presented by this case. For the Fourth Amendment protects people, not places. What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection. But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.

    The Government stresses the fact that the telephone booth from which the petitioner made his calls was constructed partly of glass, so that he was as visible after he entered it as he would have been if he had remained outside. But what he sought to exclude when he entered the booth was not the intruding eye—it was the uninvited ear. He did not shed his right to do so simply because he made his calls from a place where he might be seen. No less than an individual in a business office, in a friend’s apartment, or in a taxicab, a person in a telephone booth may rely upon the protection of the Fourth Amendment. One who occupies it, shuts the door behind him, and pays the toll that permits him to place a call is surely entitled to assume that the words he utters into the mouthpiece will not be broadcast to the world. To read the Constitution more narrowly is to ignore the vital role that the public telephone has come to play in private communication.

    The Government contends, however, that the activities of its agents in this case should not be tested by Fourth Amendment requirements, for the surveillance technique they employed involved no physical penetration of the telephone booth from which the petitioner placed his calls. It is true that the absence of such penetration was at one time thought to foreclose further Fourth Amendment inquiry, Olmstead v. United States, 277 U.S. 438; Goldman v. United States, 316 U.S. 129, 134—136, for that Amendment was thought to limit only searches and seizures of tangible property. But “(t)he premise that property interests control the right of the Government to search and seize has been discredited.” Thus, although a closely divided Court supposed in Olmstead that surveillance without any trespass and without the seizure of any material object fell outside the ambit of the Constitution, we have since departed from the narrow view on which that decision rested. Indeed, we have expressly held that the Fourth Amendment governs not only the seizure of tangible items, but extends as well to the recording of oral statements overheard without any “technical trespass under … local property law.” Once this much is acknowledged, and once it is recognized that the Fourth Amendment protects people—and not simply “areas”—against unreasonable searches and seizures it becomes clear that the reach of that Amendment cannot turn upon the presence or absence of a physical intrusion into any given enclosure.

    We conclude that the underpinnings of Olmstead and Goldman have been so eroded by our subsequent decisions that the “trespass” doctrine there enunciated can no longer be regarded as controlling. The Government’s activities in electronically listening to and recording the petitioner’s words violated the privacy upon which he justifiably relied while using the telephone booth and thus constituted a “search and seizure” within the meaning of the Fourth Amendment. The fact that the electronic device employed to achieve that end did not happen to penetrate the wall of the booth can have no constitutional significance.

    Wherever a man may be, he is entitled to know that he will remain free from unreasonable searches and seizures. The government agents here ignored “the procedure of antecedent justification … that is central to the Fourth Amendment,” a procedure that we hold to be a constitutional precondition of the kind of electronic surveillance involved in this case. Because the surveillance here failed to meet that condition, and because it led to the petitioner’s conviction, the judgment must be reversed.

    Mr. Justice MARSHALL took no part in the consideration or decision of this case.

    Mr. Justice HARLAN, concurring.

    I join the opinion of the Court, which I read to hold only (a) that an enclosed telephone booth is an area where, like a home, a person has a constitutionally protected reasonable expectation of privacy; (b) that electronic as well as physical intrusion into a place that is in this sense private may constitute a violation of the Fourth Amendment; and (c) that the invasion of a constitutionally protected area by federal authorities is, as the Court has long held, presumptively unreasonable in the absence of a search warrant.

    As the Court’s opinion states, “the Fourth Amendment protects people, not places.” The question, however, is what protection it affords to those people. Generally, as here, the answer to that question requires reference to a “place.” My understanding of the rule that has emerged from prior decisions is that there is a twofold requirement, first that a person have exhibited an actual (subjective) expectation of privacy and, second, that the expectation be one that society is prepared to recognize as “reasonable.” Thus a man’s home is, for most purposes, a place where he expects privacy, but objects, activities, or statements that he exposes to the “plain view” of outsiders are not “protected” because no intention to keep them to himself has been exhibited. On the other hand, conversations in the open would not be protected against being overheard, for the expectation of privacy under the circumstances would be unreasonable.

    The critical fact in this case is that “(o)ne who occupies it, (a telephone booth) shuts the door behind him, and pays the toll that permits him to place a call is surely entitled to assume” that his conversation is not being intercepted. The point is not that the booth is “accessible to the public” at other times, but that it is a temporarily private place whose momentary occupants’ expectations of freedom from intrusion are recognized as reasonable.

    Finally, I do not read the Court’s opinion to declare that no interception of a conversation one-half of which occurs in a public telephone booth can be reasonable in the absence of a warrant. As elsewhere under the Fourth Amendment, warrants are the general rule, to which the legitimate needs of law enforcement may demand specific exceptions. It will be time enough to consider any such exceptions when an appropriate occasion presents itself, and I agree with the Court that this is not one.

    Mr. Justice BLACK, dissenting.

    If I could agree with the Court that eavesdropping carried on by electronic means (equivalent to wiretapping) constitutes a “search” or “seizure,” I would be happy to join the Court’s opinion.

    My basic objection is twofold: (1) I do not believe that the words of the Amendment will bear the meaning given them by today’s decision, and (2) I do not believe that it is the proper role of this Court to rewrite the Amendment in order “to bring it into harmony with the times” and thus reach a result that many people believe to be desirable.

    While I realize that an argument based on the meaning of words lacks the scope, and no doubt the appeal, of broad policy discussions and philosophical discourses on such nebulous subjects as privacy, for me the language of the Amendment is the crucial place to look in construing a written document such as our Constitution. The Fourth Amendment says that

    “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”

    The first clause protects “persons, houses, papers, and effects, against unreasonable searches and seizures ….” These words connote the idea of tangible things with size, form, and weight, things capable of being searched, seized, or both. The second clause of the Amendment still further establishes its Framers’ purpose to limit its protection to tangible things by providing that no warrants shall issue but those “particularly describing the place to be searched, and the persons or things to be seized.” A conversation overheard by eavesdropping, whether by plain snooping or wiretapping, is not tangible and, under the normally accepted meanings of the words, can neither be searched nor seized. In addition, the language of the second clause indicates that the Amendment refers not only to something tangible so it can be seized but to something already in existence so it can be described. Yet the Court’s interpretation would have the Amendment apply to overhearing future conversations which by their very nature are nonexistent until they take place. How can one “describe” a future conversation, and, if one cannot, how can a magistrate issue a warrant to eavesdrop one in the future? It is argued that information showing what is expected to be said is sufficient to limit the boundaries of what later can be admitted into evidence; but does such general information really meet the specific language of the Amendment which says “particularly describing”? Rather than using language in a completely artificial way, I must conclude that the Fourth Amendment simply does not apply to eavesdropping.

    Tapping telephone wires, of course, was an unknown possibility at the time the Fourth Amendment was adopted. But eavesdropping (and wiretapping is nothing more than eavesdropping by telephone) was, as even the majority opinion in Berger, supra, recognized, “an ancient practice which at common law was condemned as a nuisance. In those days the eavesdropper listened by naked ear under the eaves of houses or their windows, or beyond their walls seeking out private discourse.” There can be no doubt that the Framers were aware of this practice, and if they had desired to outlaw or restrict the use of evidence obtained by eavesdropping, I believe that they would have used the appropriate language to do so in the Fourth Amendment. They certainly would not have left such a task to the ingenuity of language-stretching judges. No one, it seems to me, can read the debates on the Bill of Rights without reaching the conclusion that its Framers and critics well knew the meaning of the words they used, what they would be understood to mean by others, their scope and their limitations. Under these circumstances it strikes me as a charge against their scholarship, their common sense and their candor to give to the Fourth Amendment’s language the eavesdropping meaning the Court imputes to it today.

    I do not deny that common sense requires and that this Court often has said that the Bill of Rights’ safeguards should be given a liberal construction. This principle, however, does not justify construing the search and seizure amendment as applying to eavesdropping or the “seizure” of conversations. The Fourth Amendment was aimed directly at the abhorred practice of breaking in, ransacking and searching homes and other buildings and seizing people’s personal belongings without warrants issued by magistrates. The Amendment deserves, and this Court has given it, a liberal construction in order to protect against warrantless searches of buildings and seizures of tangible personal effects. But until today this Court has refused to say that eavesdropping comes within the ambit of Fourth Amendment restrictions.

    Since I see no way in which the words of the Fourth Amendment can be construed to apply to eavesdropping, that closes the matter for me. In interpreting the Bill of Rights, I willingly go as far as a liberal construction of the language takes me, but I simply cannot in good conscience give a meaning to words which they have never before been thought to have and which they certainly do not have in common ordinary usage. I will not distort the words of the Amendment in order to “keep the Constitution up to date” or “to bring it into harmony with the times.” It was never meant that this Court have such power, which in effect would make us a continuously functioning constitutional convention.

    With this decision the Court has completed, I hope, its rewriting of the Fourth Amendment, which started only recently when the Court began referring incessantly to the Fourth Amendment not so much as a law against unreasonable searches and seizures as one to protect an individual’s privacy. By clever word juggling the Court finds it plausible to argue that language aimed specifically at searches and seizures of things that can be searched and seized may, to protect privacy, be applied to eavesdropped evidence of conversations that can neither be searched nor seized. Few things happen to an individual that do not affect his privacy in one way or another. Thus, by arbitrarily substituting the Court’s language, designed to protect privacy, for the Constitution’s language, designed to protect against unreasonable searches and seizures, the Court has made the Fourth Amendment its vehicle for holding all laws violative of the Constitution which offend the Court’s broadest concept of privacy.

    The Fourth Amendment protects privacy only to the extent that it prohibits unreasonable searches and seizures of “persons, houses, papers, and effects.” No general right is created by the Amendment so as to give this Court the unlimited power to hold unconstitutional everything which affects privacy. Certainly the Framers, well acquainted as they were with the excesses of governmental power, did not intend to grant this Court such omnipotent lawmaking authority as that. The history of governments proves that it is dangerous to freedom to repose such powers in courts.

    For these reasons I respectfully dissent.

    Notes, Comments, and Questions

    In Katz, the Court made clear that a physical trespass is not essential to a Fourth Amendment search. In subsequent chapters, students will explore the Court’s efforts to flesh out this ruling, applying it to contexts such as police officers flying over houses, police officers using thermal imaging devices to examine a home, and police searching garbage left outside for collection.

    In our next case, however, the Court reminds readers that although trespass is not necessary to a Fourth Amendment search, it can be sufficient. That is, although the line of cases following Katz remains essential reading for a student of criminal procedure, not every Fourth Amendment search necessarily invades a person’s reasonable expectation of privacy. Forty-five years after the Court decided Katz, the Justices handed down United States v. Jones, reiterating the importance of the law of trespass to the Court’s vision of the Fourth Amendment.

    Supreme Court of the United States

    United States v. Antoine Jones

    Decided Jan. 23, 2012—565 U.S. 400

    Justice SCALIA delivered the opinion of the Court.

    We decide whether the attachment of a Global-Positioning-System (GPS) tracking device to an individual’s vehicle, and subsequent use of that device to monitor the vehicle’s movements on public streets, constitutes a search or seizure within the meaning of the Fourth Amendment.


    In 2004 respondent Antoine Jones, owner and operator of a nightclub in the District of Columbia, came under suspicion of trafficking in narcotics and was made the target of an investigation by a joint FBI and Metropolitan Police Department task force.

    [A]gents installed a GPS tracking device on the undercarriage of the Jeep while it was parked in a public parking lot. Over the next 28 days, the Government used the device to track the vehicle’s movements, and once had to replace the device’s battery. By means of signals from multiple satellites, the device established the vehicle’s location within 50 to 100 feet, and communicated that location by cellular phone to a Government computer. It relayed more than 2,000 pages of data over the 4-week period.

    The Government ultimately obtained a multiple-count indictment charging Jones with conspiracy to distribute and possess with intent to distribute five kilograms or more of cocaine and 50 grams or more of cocaine base. Before trial, Jones filed a motion to suppress evidence obtained through the GPS device. The District Court granted the motion only in part, suppressing the data obtained while the vehicle was parked in the garage adjoining Jones’s residence. It held the remaining data admissible, because “‘[a] person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another.’”

    The Government introduced at trial the GPS-derived locational data, which connected Jones to the alleged conspirators’ stash house that contained $850,000 in cash, 97 kilograms of cocaine, and 1 kilogram of cocaine base. The jury returned a guilty verdict, and the District Court sentenced Jones to life imprisonment.

    The United States Court of Appeals for the District of Columbia Circuit reversed the conviction because of admission of the evidence obtained by warrantless use of the GPS device which, it said, violated the Fourth Amendment. The D.C. Circuit denied the Government’s petition for rehearing en banc, with four judges dissenting. We granted certiorari.


    The Fourth Amendment provides in relevant part that “[t]he right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated.” It is beyond dispute that a vehicle is an “effect” as that term is used in the Amendment. We hold that the Government’s installation of a GPS device on a target’s vehicle, and its use of that device to monitor the vehicle’s movements, constitutes a “search.”

    It is important to be clear about what occurred in this case: The Government physically occupied private property for the purpose of obtaining information. We have no doubt that such a physical intrusion would have been considered a “search” within the meaning of the Fourth Amendment when it was adopted. Entick v. Carrington, 95 Eng. Rep. 807 (C.P. 1765), is a “case we have described as a ‘monument of English freedom’ ‘undoubtedly familiar’ to ‘every American statesman’ at the time the Constitution was adopted, and considered to be ‘the true and ultimate expression of constitutional law’ ” with regard to search and seizure. In that case, Lord Camden expressed in plain terms the significance of property rights in search-and-seizure analysis:

    “[O]ur law holds the property of every man so sacred, that no man can set his foot upon his neighbour’s close without his leave; if he does he is a trespasser, though he does no damage at all; if he will tread upon his neighbour’s ground, he must justify it by law.”

    The text of the Fourth Amendment reflects its close connection to property, since otherwise it would have referred simply to “the right of the people to be secure against unreasonable searches and seizures”; the phrase “in their persons, houses, papers, and effects” would have been superfluous.

    Consistent with this understanding, our Fourth Amendment jurisprudence was tied to common-law trespass, at least until the latter half of the 20th century. Thus, in Olmstead v. United States, 277 U.S. 438, we held that wiretaps attached to telephone wires on the public streets did not constitute a Fourth Amendment search because “[t]here was no entry of the houses or offices of the defendants.”

    Our later cases, of course, have deviated from that exclusively property-based approach. In Katz v. United States, we said that “the Fourth Amendment protects people, not places,” and found a violation in attachment of an eavesdropping device to a public telephone booth. Our later cases have applied the analysis of Justice Harlan’s concurrence in that case, which said that a violation occurs when government officers violate a person’s “reasonable expectation of privacy.”

    The Government contends that the Harlan standard shows that no search occurred here, since Jones had no “reasonable expectation of privacy” in the area of the Jeep accessed by Government agents (its underbody) and in the locations of the Jeep on the public roads, which were visible to all. But we need not address the Government’s contentions, because Jones’s Fourth Amendment rights do not rise or fall with the Katz formulation. At bottom, we must “assur[e] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.” As explained, for most of our history the Fourth Amendment was understood to embody a particular concern for government trespass upon the areas (“persons, houses, papers, and effects”) it enumerates. Katz did not repudiate that understanding. Less than two years later the Court upheld defendants’ contention that the Government could not introduce against them conversations between other people obtained by warrantless placement of electronic surveillance devices in their homes. The opinion rejected the dissent’s contention that there was no Fourth Amendment violation “unless the conversational privacy of the homeowner himself is invaded.” Alderman v. United States, 394 U.S. 165, 176 (1969). “[W]e [do not] believe that Katz, by holding that the Fourth Amendment protects persons and their private conversations, was intended to withdraw any of the protection which the Amendment extends to the home….” Id., at 180.

    More recently, in Soldal v. Cook County, 506 U.S. 56 (1992), the Court unanimously rejected the argument that although a “seizure” had occurred “in a ‘technical’ sense” when a trailer home was forcibly removed, no Fourth Amendment violation occurred because law enforcement had not “invade[d] the [individuals’] privacy.” Katz, the Court explained, established that “property rights are not the sole measure of Fourth Amendment violations,” but did not “snuf[f] out the previously recognized protection for property.” As Justice Brennan explained in his concurrence in Knotts, Katz did not erode the principle “that, when the Government does engage in physical intrusion of a constitutionally protected area in order to obtain information, that intrusion may constitute a violation of the Fourth Amendment.” We have embodied that preservation of past rights in our very definition of “reasonable expectation of privacy” which we have said to be an expectation “that has a source outside of the Fourth Amendment, either by reference to concepts of real or personal property law or to understandings that are recognized and permitted by society.” Katz did not narrow the Fourth Amendment’s scope.

    The Government contends that several of our post-Katz cases foreclose the conclusion that what occurred here constituted a search. It relies principally on two cases in which we rejected Fourth Amendment challenges to “beepers,” electronic tracking devices that represent another form of electronic monitoring. The first case, Knotts, upheld against Fourth Amendment challenge the use of a “beeper” that had been placed in a container of chloroform, allowing law enforcement to monitor the location of the container. We said that there had been no infringement of Knotts’ reasonable expectation of privacy since the information obtained—the location of the automobile carrying the container on public roads, and the location of the off-loaded container in open fields near Knotts’ cabin—had been voluntarily conveyed to the public. But as we have discussed, the Katz reasonable-expectation-of-privacy test has been added to, not substituted for, the common-law trespassory test. The holding in Knotts addressed only the former, since the latter was not at issue. The beeper had been placed in the container before it came into Knotts’ possession, with the consent of the then-owner. Knotts did not challenge that installation, and we specifically declined to consider its effect on the Fourth Amendment analysis. Knotts would be relevant, perhaps, if the Government were making the argument that what would otherwise be an unconstitutional search is not such where it produces only public information. The Government does not make that argument, and we know of no case that would support it.

    The second “beeper” case, United States v. Karo, 468 U.S. 705 (1984), does not suggest a different conclusion. There we addressed the question left open by Knotts, whether the installation of a beeper in a container amounted to a search or seizure. As in Knotts, at the time the beeper was installed the container belonged to a third party, and it did not come into possession of the defendant until later. Thus, the specific question we considered was whether the installation “with the consent of the original owner constitute[d] a search or seizure … when the container is delivered to a buyer having no knowledge of the presence of the beeper.” We held not. The Government, we said, came into physical contact with the container only before it belonged to the defendant Karo; and the transfer of the container with the unmonitored beeper inside did not convey any information and thus did not invade Karo’s privacy. That conclusion is perfectly consistent with the one we reach here. Karo accepted the container as it came to him, beeper and all, and was therefore not entitled to object to the beeper’s presence, even though it was used to monitor the container’s location. Cf. On Lee v. United States, 343 U.S. 747 (1952) (no search or seizure where an informant, who was wearing a concealed microphone, was invited into the defendant’s business). Jones, who possessed the Jeep at the time the Government trespassorily inserted the information-gathering device, is on much different footing.

    The Government also points to our exposition in New York v. Class, 475 U.S. 106 (1986), that “[t]he exterior of a car … is thrust into the public eye, and thus to examine it does not constitute a ‘search.’” That statement is of marginal relevance here since, as the Government acknowledges, “the officers in this case did more than conduct a visual inspection of respondent’s vehicle.” By attaching the device to the Jeep, officers encroached on a protected area. In Class itself we suggested that this would make a difference, for we concluded that an officer’s momentary reaching into the interior of a vehicle did constitute a search.

    Finally, the Government’s position gains little support from our conclusion in Oliver v. United States, 466 U.S. 170 (1984), that officers’ information-gathering intrusion on an “open field” did not constitute a Fourth Amendment search even though it was a trespass at common law. Quite simply, an open field, unlike the curtilage of a home, is not one of those protected areas enumerated in the Fourth Amendment. The Government’s physical intrusion on such an area—unlike its intrusion on the “effect” at issue here—is of no Fourth Amendment significance.


    The concurrence begins by accusing us of applying “18th-century tort law.” That is a distortion. What we apply is an 18th-century guarantee against unreasonable searches, which we believe must provide at a minimum the degree of protection it afforded when it was adopted. The concurrence does not share that belief. It would apply exclusively Katz’s reasonable-expectation-of-privacy test, even when that eliminates rights that previously existed.

    The concurrence [by Justice Alito] faults our approach for “present[ing] particularly vexing problems” in cases that do not involve physical contact, such as those that involve the transmission of electronic signals. We entirely fail to understand that point. For unlike the concurrence, which would make Katz the exclusive test, we do not make trespass the exclusive test. Situations involving merely the transmission of electronic signals without trespass would remain subject to Katz analysis.

    In fact, it is the concurrence’s insistence on the exclusivity of the Katz test that needlessly leads us into “particularly vexing problems” in the present case. This Court has to date not deviated from the understanding that mere visual observation does not constitute a search. We accordingly held in Knotts that “[a] person traveling in an automobile on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another.” Thus, even assuming that the concurrence is correct to say that “[t]raditional surveillance” of Jones for a 4–week period “would have required a large team of agents, multiple vehicles, and perhaps aerial assistance,” our cases suggest that such visual observation is constitutionally permissible. It may be that achieving the same result through electronic means, without an accompanying trespass, is an unconstitutional invasion of privacy, but the present case does not require us to answer that question.

    And answering it affirmatively leads us needlessly into additional thorny problems. The concurrence posits that “relatively short-term monitoring of a person’s movements on public streets” is okay, but that “the use of longer term GPS monitoring in investigations of most offenses” is no good. That introduces yet another novelty into our jurisprudence. There is no precedent for the proposition that whether a search has occurred depends on the nature of the crime being investigated. And even accepting that novelty, it remains unexplained why a 4–week investigation is “surely” too long and why a drug-trafficking conspiracy involving substantial amounts of cash and narcotics is not an “extraordinary offens[e]” which may permit longer observation. What of a 2–day monitoring of a suspected purveyor of stolen electronics? Or of a 6–month monitoring of a suspected terrorist? We may have to grapple with these “vexing problems” in some future case where a classic trespassory search is not involved and resort must be had to Katz analysis; but there is no reason for rushing forward to resolve them here.

    The judgment of the Court of Appeals for the D.C. Circuit is affirmed.

    Justice SOTOMAYOR, concurring.

    I join the Court’s opinion because I agree that a search within the meaning of the Fourth Amendment occurs, at a minimum, “[w]here, as here, the Government obtains information by physically intruding on a constitutionally protected area.” “[W]hen the Government does engage in physical intrusion of a constitutionally protected area in order to obtain information, that intrusion may constitute a violation of the Fourth Amendment.”

    Nonetheless, as Justice ALITO notes, physical intrusion is now unnecessary to many forms of surveillance. With increasing regularity, the Government will be capable of duplicating the monitoring undertaken in this case by enlisting factory- or owner-installed vehicle tracking devices or GPS-enabled smartphones. In cases of electronic or other novel modes of surveillance that do not depend upon a physical invasion on property, the majority opinion’s trespassory test may provide little guidance. But “[s]ituations involving merely the transmission of electronic signals without trespass would remain subject to Katz analysis.” As Justice ALITO incisively observes, the same technological advances that have made possible nontrespassory surveillance techniques will also affect the Katz test by shaping the evolution of societal privacy expectations. Under that rubric, I agree with Justice ALITO that, at the very least, “longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy.”

    In cases involving even short-term monitoring, some unique attributes of GPS surveillance relevant to the Katz analysis will require particular attention. GPS monitoring generates a precise, comprehensive record of a person’s public movements that reflects a wealth of detail about her familial, political, professional, religious, and sexual associations. The Government can store such records and efficiently mine them for information years into the future. And because GPS monitoring is cheap in comparison to conventional surveillance techniques and, by design, proceeds surreptitiously, it evades the ordinary checks that constrain abusive law enforcement practices: “limited police resources and community hostility.”

    Awareness that the Government may be watching chills associational and expressive freedoms. And the Government’s unrestrained power to assemble data that reveal private aspects of identity is susceptible to abuse. The net result is that GPS monitoring—by making available at a relatively low cost such a substantial quantum of intimate information about any person whom the Government, in its unfettered discretion, chooses to track—may “alter the relationship between citizen and government in a way that is inimical to democratic society.”

    I would take these attributes of GPS monitoring into account when considering the existence of a reasonable societal expectation of privacy in the sum of one’s public movements. I would ask whether people reasonably expect that their movements will be recorded and aggregated in a manner that enables the Government to ascertain, more or less at will, their political and religious beliefs, sexual habits, and so on. I do not regard as dispositive the fact that the Government might obtain the fruits of GPS monitoring through lawful conventional surveillance techniques. I would also consider the appropriateness of entrusting to the Executive, in the absence of any oversight from a coordinate branch, a tool so amenable to misuse, especially in light of the Fourth Amendment’s goal to curb arbitrary exercises of police power to and prevent “a too permeating police surveillance.”

    More fundamentally, it may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties. This approach is ill suited to the digital age, in which people reveal a great deal of information about themselves to third parties in the course of carrying out mundane tasks. People disclose the phone numbers that they dial or text to their cellular providers; the URLs that they visit and the e-mail addresses with which they correspond to their Internet service providers; and the books, groceries, and medications they purchase to online retailers. Perhaps, as Justice ALITO notes, some people may find the “tradeoff” of privacy for convenience “worthwhile,” or come to accept this “diminution of privacy” as “inevitable,” and perhaps not. I for one doubt that people would accept without complaint the warrantless disclosure to the Government of a list of every Web site they had visited in the last week, or month, or year. But whatever the societal expectations, they can attain constitutionally protected status only if our Fourth Amendment jurisprudence ceases to treat secrecy as a prerequisite for privacy. I would not assume that all information voluntarily disclosed to some member of the public for a limited purpose is, for that reason alone, disentitled to Fourth Amendment protection.

    Resolution of these difficult questions in this case is unnecessary, however, because the Government’s physical intrusion on Jones’ Jeep supplies a narrower basis for decision. I therefore join the majority’s opinion.

    Justice ALITO, with whom Justice GINSBURG, Justice BREYER, and Justice KAGAN join, concurring in the judgment.

    This case requires us to apply the Fourth Amendment’s prohibition of unreasonable searches and seizures to a 21st-century surveillance technique, the use of a Global Positioning System (GPS) device to monitor a vehicle’s movements for an extended period of time. Ironically, the Court has chosen to decide this case based on 18th-century tort law.

    This holding, in my judgment, is unwise. It strains the language of the Fourth Amendment; it has little if any support in current Fourth Amendment case law; and it is highly artificial.

    I would analyze the question presented in this case by asking whether respondent’s reasonable expectations of privacy were violated by the long-term monitoring of the movements of the vehicle he drove.


    The Fourth Amendment prohibits “unreasonable searches and seizures,” and the Court makes very little effort to explain how the attachment or use of the GPS device fits within these terms. The Court does not contend that there was a seizure … and here there was none.

    The Court does claim that the installation and use of the GPS constituted a search, but this conclusion is dependent on the questionable proposition that these two procedures cannot be separated for purposes of Fourth Amendment analysis. If these two procedures are analyzed separately, it is not at all clear from the Court’s opinion why either should be regarded as a search. It is clear that the attachment of the GPS device was not itself a search; if the device had not functioned or if the officers had not used it, no information would have been obtained. And the Court does not contend that the use of the device constituted a search either. On the contrary, the Court accepts the holding in United States v. Knotts, 460 U.S. 276, that the use of a surreptitiously planted electronic device to monitor a vehicle’s movements on public roads did not amount to a search.

    The Court argues—and I agree—that “we must ‘assur[e] preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.’” But it is almost impossible to think of late–18th-century situations that are analogous to what took place in this case. (Is it possible to imagine a case in which a constable secreted himself somewhere in a coach and remained there for a period of time in order to monitor the movements of the coach’s owner?1) The Court’s theory seems to be that the concept of a search, as originally understood, comprehended any technical trespass that led to the gathering of evidence, but we know that this is incorrect. At common law, any unauthorized intrusion on private property was actionable but a trespass on open fields, as opposed to the “curtilage” of a home, does not fall within the scope of the Fourth Amendment because private property outside the curtilage is not part of a “hous[e]” within the meaning of the Fourth Amendment.


    The Court’s reasoning in this case is very similar to that in the Court’s early decisions involving wiretapping and electronic eavesdropping, namely, that a technical trespass followed by the gathering of evidence constitutes a search. In the early electronic surveillance cases, the Court concluded that a Fourth Amendment search occurred when private conversations were monitored as a result of an “unauthorized physical penetration into the premises occupied” by the defendant. Silverman v. United States, 365 U.S. 505, 509 (1961). In Silverman, police officers listened to conversations in an attached home by inserting a “spike mike” through the wall that this house shared with the vacant house next door. This procedure was held to be a search because the mike made contact with a heating duct on the other side of the wall and thus “usurp[ed] … an integral part of the premises.”

    By contrast, in cases in which there was no trespass, it was held that there was no search. Thus, in Olmstead v. United States, 277 U.S. 438 (1928), the Court found that the Fourth Amendment did not apply because “[t]he taps from house lines were made in the streets near the houses.” Similarly, the Court concluded that no search occurred in Goldman v. United States, 316 U.S. 129 (1942), where a “detectaphone” was placed on the outer wall of defendant’s office for the purpose of overhearing conversations held within the room.

    This trespass-based rule was repeatedly criticized. In Olmstead, Justice Brandeis wrote that it was “immaterial where the physical connection with the telephone wires was made.”

    Katz v. United States, 389 U.S. 347 (1967), finally did away with the old approach, holding that a trespass was not required for a Fourth Amendment violation. [T]he Katz Court, “repudiate[ed]” the old doctrine and held that “[t]he fact that the electronic device employed … did not happen to penetrate the wall of the booth can have no constitutional significance.” What mattered, the Court held, was whether the conduct at issue “violated the privacy upon which [the defendant] justifiably relied while using the telephone booth.”

    Under this approach, as the Court later put it when addressing the relevance of a technical trespass, “an actual trespass is neither necessary nor sufficient to establish a constitutional violation.”

    [T]he majority is hard pressed to find support in post-Katz cases for its trespass-based theory.


    Disharmony with a substantial body of existing case law is only one of the problems with the Court’s approach in this case.

    I will briefly note four others. First, the Court’s reasoning largely disregards what is really important (the use of a GPS for the purpose of long-term tracking) and instead attaches great significance to something that most would view as relatively minor (attaching to the bottom of a car a small, light object that does not interfere in any way with the car’s operation). Attaching such an object is generally regarded as so trivial that it does not provide a basis for recovery under modern tort law. But under the Court’s reasoning, this conduct may violate the Fourth Amendment. By contrast, if long-term monitoring can be accomplished without committing a technical trespass—suppose, for example, that the Federal Government required or persuaded auto manufacturers to include a GPS tracking device in every car—the Court’s theory would provide no protection.

    Second, the Court’s approach leads to incongruous results. If the police attach a GPS device to a car and use the device to follow the car for even a brief time, under the Court’s theory, the Fourth Amendment applies. But if the police follow the same car for a much longer period using unmarked cars and aerial assistance, this tracking is not subject to any Fourth Amendment constraints.

    In the present case, the Fourth Amendment applies, the Court concludes, because the officers installed the GPS device after respondent’s wife, to whom the car was registered, turned it over to respondent for his exclusive use. But if the GPS had been attached prior to that time, the Court’s theory would lead to a different result. The Court proceeds on the assumption that respondent “had at least the property rights of a bailee,” but a bailee may sue for a trespass to chattel only if the injury occurs during the term of the bailment. So if the GPS device had been installed before respondent’s wife gave him the keys, respondent would have no claim for trespass—and, presumably, no Fourth Amendment claim either.

    Third, under the Court’s theory, the coverage of the Fourth Amendment may vary from State to State. If the events at issue here had occurred in a community property State or a State that has adopted the Uniform Marital Property Act, respondent would likely be an owner of the vehicle, and it would not matter whether the GPS was installed before or after his wife turned over the keys. In non-community-property States, on the other hand, the registration of the vehicle in the name of respondent’s wife would generally be regarded as presumptive evidence that she was the sole owner.

    Fourth, the Court’s reliance on the law of trespass will present particularly vexing problems in cases involving surveillance that is carried out by making electronic, as opposed to physical, contact with the item to be tracked. For example, suppose that the officers in the present case had followed respondent by surreptitiously activating a stolen vehicle detection system that came with the car when it was purchased. Would the sending of a radio signal to activate this system constitute a trespass to chattels? Trespass to chattels has traditionally required a physical touching of the property. In recent years, courts have wrestled with the application of this old tort in cases involving unwanted electronic contact with computer systems, and some have held that even the transmission of electrons that occurs when a communication is sent from one computer to another is enough. But may such decisions be followed in applying the Court’s trespass theory? Assuming that what matters under the Court’s theory is the law of trespass as it existed at the time of the adoption of the Fourth Amendment, do these recent decisions represent a change in the law or simply the application of the old tort to new situations?


    The Katz expectation-of-privacy test avoids the problems and complications noted above, but it is not without its own difficulties. It involves a degree of circularity, and judges are apt to confuse their own expectations of privacy with those of the hypothetical reasonable person to which the Katz test looks. In addition, the Katz test rests on the assumption that this hypothetical reasonable person has a well-developed and stable set of privacy expectations. But technology can change those expectations. Dramatic technological change may lead to periods in which popular expectations are in flux and may ultimately produce significant changes in popular attitudes. New technology may provide increased convenience or security at the expense of privacy, and many people may find the tradeoff worthwhile. And even if the public does not welcome the diminution of privacy that new technology entails, they may eventually reconcile themselves to this development as inevitable.

    On the other hand, concern about new intrusions on privacy may spur the enactment of legislation to protect against these intrusions. This is what ultimately happened with respect to wiretapping. After Katz, Congress did not leave it to the courts to develop a body of Fourth Amendment case law governing that complex subject. Instead, Congress promptly enacted a comprehensive statute and since that time, the regulation of wiretapping has been governed primarily by statute and not by case law.


    Recent years have seen the emergence of many new devices that permit the monitoring of a person’s movements. In some locales, closed-circuit television video monitoring is becoming ubiquitous. On toll roads, automatic toll collection systems create a precise record of the movements of motorists who choose to make use of that convenience. Many motorists purchase cars that are equipped with devices that permit a central station to ascertain the car’s location at any time so that roadside assistance may be provided if needed and the car may be found if it is stolen.

    Perhaps most significant, cell phones and other wireless devices now permit wireless carriers to track and record the location of users—and as of June 2011, it has been reported, there were more than 322 million wireless devices in use in the United States. For older phones, the accuracy of the location information depends on the density of the tower network, but new “smart phones,” which are equipped with a GPS device, permit more precise tracking. For example, when a user activates the GPS on such a phone, a provider is able to monitor the phone’s location and speed of movement and can then report back real-time traffic conditions after combining (“crowdsourcing”) the speed of all such phones on any particular road. Similarly, phone-location-tracking services are offered as “social” tools, allowing consumers to find (or to avoid) others who enroll in these services. The availability and use of these and other new devices will continue to shape the average person’s expectations about the privacy of his or her daily movements.


    In the pre-computer age, the greatest protections of privacy were neither constitutional nor statutory, but practical. Traditional surveillance for any extended period of time was difficult and costly and therefore rarely undertaken. The surveillance at issue in this case—constant monitoring of the location of a vehicle for four weeks—would have required a large team of agents, multiple vehicles, and perhaps aerial assistance. Only an investigation of unusual importance could have justified such an expenditure of law enforcement resources. Devices like the one used in the present case, however, make long-term monitoring relatively easy and cheap. In circumstances involving dramatic technological change, the best solution to privacy concerns may be legislative. A legislative body is well situated to gauge changing public attitudes, to draw detailed lines, and to balance privacy and public safety in a comprehensive way.

    To date, however, Congress and most States have not enacted statutes regulating the use of GPS tracking technology for law enforcement purposes. The best that we can do in this case is to apply existing Fourth Amendment doctrine and to ask whether the use of GPS tracking in a particular case involved a degree of intrusion that a reasonable person would not have anticipated.

    Under this approach, relatively short-term monitoring of a person’s movements on public streets accords with expectations of privacy that our society has recognized as reasonable. But the use of longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy. For such offenses, society’s expectation has been that law enforcement agents and others would not—and indeed, in the main, simply could not—secretly monitor and catalogue every single movement of an individual’s car for a very long period. In this case, for four weeks, law enforcement agents tracked every movement that respondent made in the vehicle he was driving. We need not identify with precision the point at which the tracking of this vehicle became a search, for the line was surely crossed before the 4–week mark. Other cases may present more difficult questions. But where uncertainty exists with respect to whether a certain period of GPS surveillance is long enough to constitute a Fourth Amendment search, the police may always seek a warrant. We also need not consider whether prolonged GPS monitoring in the context of investigations involving extraordinary offenses would similarly intrude on a constitutionally protected sphere of privacy. In such cases, long-term tracking might have been mounted using previously available techniques.

    For these reasons, I conclude that the lengthy monitoring that occurred in this case constituted a search under the Fourth Amendment. I therefore agree with the majority that the decision of the Court of Appeals must be affirmed.

    Notes, Comments, and Questions

    Although the Jones Court held that Katz is not the sole touchstone of Fourth Amendment “search” analysis, it also made clear that Katz has not in any way been overruled. When considering whether certain state action constitutes a “search,” students should consider both whether it satisfies the criteria set forth in Katz and whether it satisfies the more recent standard articulated in Jones. A person complaining about state action need not satisfy both standards; either one will do.

    As Justice Alito noted in his concurrence, “the regulation of wiretapping has been governed primarily by statute and not by case law.” This is the first example of what will become a common theme in the course. Put simply, much of criminal procedure—like criminal law more generally—is not regulated by constitutional law. Witness identification procedures, for example, are largely left to the discretion of police departments, with minimal oversight by courts. Once states meet bare minimum standards for providing the assistance of counsel for indigent defendants, they decide how much additional money to devote to the effort. States decide how many police officers they want to patrol various neighborhoods, how strictly to enforce various criminal laws, and how much to punish convicted defendants. As the semester progresses, students should pay careful attention to the policy decisions not dictated by Supreme Court doctrine. Those are decisions that, after students become lawyers, they may have the opportunity to guide.

    The majority in Jones relies on the trespassory nature of the police contact with the jeep to find a search rather than a Katz-style “reasonable expectation of privacy” analysis. As Justice Sotomayor predicted, though, police surveillance of GPS-enabled smartphones without trespassory invasion has quickly become a reality, and police can now access this data without a physical trespass. Moreover, police can obtain GPS information about all cell phone users in a particular area. Consider the “reverse location search warrant.” This warrant allows police, without touching anyone’s phone, to gather cell phone GPS data on all phones within the vicinity of a crime. Is this tactic a search under Jones? Under Katz? Why or why not? Consider the reasonable expectations of privacy for private individuals who are in the general locality of a crime by happenstance.

    What result if the police do not trespass to place the GPS, but instead local ordinances or state legislation requires vehicles to be outfitted with GPS? Consider a Chicago ordinance that requires all food trucks to be outfitted with GPS and allows the city to access that GPS data for six months without a warrant.

    One final note: In 2018, the Supreme Court decided Carpenter v. United States, 138 S. Ct. 2206 (2018), a case concerning “whether the Government conducts a search under the Fourth Amendment when it accesses historical cell phone records that provide a comprehensive chronicle of the user’s past movements.” Students should consider now (and perhaps write down) how they would answer this question, using the reasoning set forth in Katz and Jones. In the next few chapters, students will read several cases in which the Court applies the doctrines of Katz and Jones to different scenarios. Then, in Chapter 5, the Court’s decision in Carpenter is presented. Will the Court’s reasoning match yours?