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Scope of the Rights Protected by the Fourth Amendment

Under the Fourth Amendment, law enforcement officers cannot conduct an “unreasonable” search of someone’s person or property. In most cases, this means the officers must have a warrant or probable cause to believe a crime has been committed. However, what “reasonable” means in this context is open to interpretation. This article provides an overview of the Supreme Court’s interpretation, as well as the different doctrines used to examine Fourth Amendment cases. 

What the Fourth Amendment Says

“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.”

What Rights Are Granted By the Fourth Amendment?

United States Library of Congress, The Constitution of the United States of America: Analysis and Interpretation

In its 1947 decision Harris v. United States,1 the Supreme Court approved as reasonable the warrantless search of a four-room apartment pursuant to the arrest of the man found there. A year later, however, a reconstituted Court majority set aside a conviction based on evidence seized by a warrantless search pursuant to an arrest and adopted the cardinal rule that, in seizing goods and articles, law enforcement agents must secure and use search warrants wherever reasonably practicable.2 This rule was set aside two years later by another reconstituted majority, which adopted the premise that the test is not whether it is reasonable to procure a search warrant, but whether the search was reasonable. Whether a search is reasonable, the Court said, must find resolution in the facts and circumstances of each case.3 However, the Court soon returned to its emphasis upon the warrant. The Fourth Amendment was in large part a reaction to the general warrants and warrantless searches that had so alienated the colonists and had helped speed the movement for independence. In the scheme of the Amendment, therefore, the requirement that ‘no Warrants shall issue, but upon probable cause,’ plays a crucial part.4 Therefore, the police must, whenever practicable, obtain advance judicial approval of searches and seizures through a warrant procedure.5 Exceptions to searches under warrants were to be closely contained by the rationale undergirding the necessity for the exception, and the scope of a search under one of the exceptions was similarly limited.6

During the 1970s the Court was closely divided on which standard to apply.7 For a while, the balance tipped in favor of the view that warrantless searches are per se unreasonable, with a few carefully prescribed exceptions.8 Gradually, guided by the variable-expectation-of-privacy approach to coverage of the Fourth Amendment, the Court broadened its view of permissible exceptions and of the scope of those exceptions.9 By 1992, it was no longer the case that the warrants-with-narrow-exceptions standard normally prevails over a reasonableness approach.10 Exceptions to the warrant requirement have multiplied, tending to confine application of the requirement to cases that are exclusively criminal in nature. And even within that core area of criminal cases, some exceptions have been broadened.

The most important category of exception is that of administrative searches justified by special needs beyond the normal need for law enforcement. Under this general rubric, the Court has upheld warrantless searches by administrative authorities in public schools, government offices, and prisons, and has upheld drug testing of public and transportation employees.11 In all of these instances, the warrant and probable cause requirements are dispensed in favor of a reasonableness standard that balances the government’s regulatory interest against the individual’s privacy interest; in all of these instances, the government’s interest has been found to outweigh the individual’s. The broad scope of the administrative search exception is evidenced by the fact that an overlap between law enforcement objectives and administrative special needs does not result in application of the warrant requirement; instead, the Court has upheld warrantless inspection of automobile junkyards and dismantling operations in spite of the strong law enforcement component of the regulation.12

In the law enforcement context, where search by warrant is still the general rule, there has also been some loosening of the requirement. For example, the scope of a valid search incident to arrest, once limited to areas within the immediate reach of the arrested suspect, was expanded to a protective sweep of the entire home, if arresting officers have a reasonable belief that the home harbors an individual who may pose a danger.13 The Court has also recognized that exigent circumstances may justify performing a blood test without a warrant on a motorist to determine his or her blood alcohol concentration (BAC).14 In another case, the Court shifted focus from whether exigent circumstances justified the failure to obtain a warrant, to whether an officer had a reasonable belief that an exception to the warrant requirement applied.15 The Court has also held that an exigent circumstances exception applied even where the exigency arose as a result of police conduct, so long as the police conduct was reasonable in that it neither threatened to nor violated the Fourth Amendment.16

Another matter of scope that the Court has addressed is the category of persons protected by the Fourth Amendment; i.e., who constitutes the people. This phrase, the Court determined, refers to a class of persons who are part of a national community or who have otherwise developed sufficient connection with [the United States] to be considered part of that community.17 The Fourth Amendment, therefore, does not apply to the search and seizure by United States agents of property that is owned by a nonresident alien and located in a foreign country. The community of protected people includes U.S. citizens who go abroad, and aliens who have voluntarily entered U.S. territory and developed substantial connections with this country. There is no resulting broad principle, however, that the Fourth Amendment constrains federal officials wherever and against whomever they act.

Early Fourth Amendment Doctrine

For the Fourth Amendment to apply to a particular set of facts, there must be a search and a seizure, occurring typically in a criminal case, with a subsequent attempt to use judicially what was seized.18 Whether there was a search and seizure within the meaning of the Amendment, and whether a complainant’s interests were constitutionally infringed, will often turn upon consideration of his interest and whether it was officially abused. What does the Amendment protect? Under the common law, there was no doubt. In Entick v. Carrington,19 Lord Camden wrote: The great end for which men entered in society was to secure their property. That right is preserved sacred and incommunicable in all instances where it has not been taken away or abridged by some public law for the good of the whole. By the laws of England, every invasion of private property, be it ever so minute, is a trespass. No man can set foot upon my ground without my license but he is liable to an action though the damage be nothing. Protection of property interests as the basis of the Fourth Amendment found easy acceptance in the Supreme Court20 and that acceptance controlled the decision in numerous cases.21 For example, in Olmstead v. United States,22 one of the two premises underlying the holding that wiretapping was not covered by the Amendment was that there had been no actual physical invasion of the defendant’s premises; where there had been an invasion—a technical trespass—electronic surveillance was deemed subject to Fourth Amendment restrictions.23

The Olmstead Case

With the invention of the microphone, the telephone, and the dictagraph recorder, it became possible to eavesdrop with much greater secrecy and expediency. Inevitably, the use of electronic devices in law enforcement was challenged, and in 1928 the Court reviewed convictions obtained on the basis of evidence gained through taps on telephone wires in violation of state law. On a five-to-four vote, the Court held that wiretapping was not within the confines of the Fourth Amendment.24 Chief Justice Taft, writing the opinion of the Court, relied on two lines of argument for the conclusion. First, because the Amendment was designed to protect one’s property interest in his premises, there was no search so long as there was no physical trespass on premises owned or controlled by a defendant. Second, all the evidence obtained had been secured by hearing, and the interception of a conversation could not qualify as a seizure, for the Amendment referred only to the seizure of tangible items. Furthermore, the violation of state law did not render the evidence excludable, since the exclusionary rule operated only on evidence seized in violation of the Constitution.25

Federal Communications Act

Six years after the decision in Olmstead, Congress enacted the Federal Communications Act and included in § 605 of the Act a broadly worded proscription on which the Court seized to place some limitation upon governmental wiretapping.26 Thus, in Nardone v. United States,27 the Court held that wiretapping by federal officers could violate § 605 if the officers both intercepted and divulged the contents of the conversation they overheard and that testimony in court would constitute a form of prohibited divulgence. Such evidence was therefore excluded, although wiretapping was not illegal under the Court’s interpretation if the information was not used outside the governmental agency. Because § 605 applied to intrastate as well as interstate transmissions,28 there was no question about the applicability of the ban to state police officers, but the Court declined to apply either the statute or the due process clause to require the exclusion of such evidence from state criminal trials.29 State efforts to legalize wiretapping pursuant to court orders were held by the Court to be precluded by the fact that Congress in § 605 had intended to occupy the field completely to the exclusion of the states.30

Nontelephonic Electronic Surveillance

The trespass rationale of Olmstead was used in cases dealing with bugging of premises rather than with tapping of telephones. Thus, in Goldman v. United States,31 the Court found no Fourth Amendment violation when a listening device was placed against a party wall so that conversations were overheard on the other side. But when officers drove a spike mike into a party wall until it came into contact with a heating duct and thus broadcast the defendant’s conversations, the Court determined that the trespass brought the case within the Amendment.32 In so holding, the Court, without alluding to the matter, overruled in effect the second rationale of Olmstead, the premise that conversations could not be seized.

The Reasonable Expectation of Privacy

The Court later adopted a new approach. The premise that property interests control the right of the government to search and seize has been discredited. We have recognized that the principal object of the Fourth Amendment is the protection of privacy rather than property, and have increasingly discarded fictional and procedural barriers rested on property concepts.33 Thus, because the Amendment protects people, not places, the requirement of actual physical trespass is dispensed with and electronic surveillance was made subject to the Amendment’s requirements.34

The new test, propounded in Katz v. United States, is whether there is an expectation of privacy upon which one may justifiably rely.35 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.36 That is, the capacity to claim the protection of the Amendment depends not upon a property right in the invaded place but upon whether the area was one in which there was reasonable expectation of freedom from governmental intrusion.37

Katz’s focus on privacy was revitalized in Kyllo v. United States,38 in which the Court invalidated the warrantless use of a thermal imaging device directed at a private home from a public street. The rule devised by the Court to limit police use of new technology that can shrink the realm of guaranteed privacy is that obtaining by sense-enhancing technology any information regarding the interior of the home that could not otherwise have been obtained without physical ‘intrusion into a constitutionally protected area’ . . . constitutes a search—at least where (as here) the technology in question is not in general public use.39 Relying on Katz, the Court rejected as mechanical the Government’s attempted distinction between off-the-wall and through-the-wall surveillance. Permitting all off-the-wall observations, the Court observed, would leave the homeowner at the mercy of advancing technology—including technology that could discern all human activity in the home. To some extent, the Court has grounded this concern about expectations of privacy in Founding-era understandings,40 explaining that the Fourth Amendment seeks to secure 'the privacies of life' against 'arbitrary power,'41 and that a central aim of the Framers was 'to place obstacles in the way of a too permeating police surveillance.'42

Although the sanctity of the home has been strongly reaffirmed, protection of privacy in other contexts becomes more problematic. A two-part test that Justice Harlan suggested in Katz often provides the starting point for analysis.43 The first element, the subjective expectation of privacy, has largely dwindled as a viable standard, because, as Justice Harlan noted in a subsequent case, our expectations, and the risks we assume, are in large part reflections of laws that translate into rules the customs and values of the past and present.44 As for the second element, whether one has a legitimate expectation of privacy that society finds reasonable to recognize, the Court has said that [l]egitimation of expectations of privacy by law must have 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.45

Thus, protection of the home is at the apex of Fourth Amendment coverage because of the right associated with ownership to exclude others;46 but ownership of other things, i.e., automobiles, does not carry a similar high degree of protection.47 That a person has taken normal precautions to maintain his privacy, that is, precautions customarily taken by those seeking to exclude others, is usually a significant factor in determining legitimacy of expectation.48 On the other hand, the Court has held that a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties.49 Some expectations, the Court has held, are simply not among those that society is prepared to accept.50 In the context of norms for the use of rapidly evolving communications devices, the Court was reluctant to consider the whole concept of privacy expectations at all, preferring other decisional grounds: The judiciary risks error by elaborating too fully on the Fourth Amendment implications of emerging technology before its role in society has become clear.51

What seems to have emerged is a balancing standard that requires an assessment of the nature of a particular practice and the likely extent of its impact on the individual’s sense of security balanced against the utility of the conduct as a technique of law enforcement. Whereas Justice Harlan saw a greater need to restrain police officers through the warrant requirement as the intrusions on individual privacy grow more extensive,52 the Court’s solicitude for law enforcement objectives frequently tilts the balance in the other direction.

Application of this balancing test, because of the Court’s weighing of law enforcement investigative needs,53 and its subjective evaluation of privacy needs, has led to the creation of a two-tier or sliding-tier scale of privacy interests. The privacy test was originally designed to permit a determination that an interest protected by the Fourth Amendment had been invaded.54 If it had been, then ordinarily a warrant was required, subject only to the narrowly defined exceptions, and the scope of the search under those exceptions was strictly tied to and justified by the circumstances which rendered its initiation permissible.55 But the Court now uses the test to determine whether the interest invaded is important or persuasive enough so that a warrant is required to justify it;56 if the individual has a lesser expectation of privacy, then the invasion may be justified, absent a warrant, by the reasonableness of the intrusion.57 Exceptions to the warrant requirement are no longer evaluated solely by the justifications for the exception, e.g., exigent circumstances, and the scope of the search is no longer tied to and limited by the justification for the exception.58 The result has been a considerable expansion, beyond what existed prior to Katz, of the power of police and other authorities to conduct searches.

The Berger and Katz Cases

In Berger v. New York,59 the Court confirmed the obsolescence of the alternative holding in Olmstead that conversations could not be seized in the Fourth Amendment sense.60 Berger held unconstitutional on its face a state eavesdropping statute under which judges were authorized to issue warrants permitting police officers to trespass on private premises to install listening devices. The warrants were to be issued upon a showing of reasonable ground to believe that evidence of crime may be thus obtained and particularly describing the person or persons whose communications, conversations or discussions are to be overheard or recorded. For the five-Justice majority, Justice Clark discerned several constitutional defects in the law. First, eavesdropping is authorized without requiring belief that any particular offense has been or is being committed; nor that the ‘property’ sought, the conversations, be particularly described.

The purpose of the probable-cause requirement of the Fourth Amendment to keep the state out of constitutionally protected areas until it has reason to believe that a specific crime has been or is being committed is thereby wholly aborted. Likewise, the statute’s failure to describe with particularity the conversations sought gives the officer a roving commission to ‘seize’ any and all conversations. It is true that the statute requires the naming of ‘the person or persons whose communications, conversations or discussions are to be overheard or recorded.’ But this does no more than identify the person whose constitutionally protected area is to be invaded rather than ‘particularly describing’ the communications, conversations, or discussions to be seized.

Secondly, authorization of eavesdropping for a two-month period is the equivalent of a series of intrusions, searches, and seizures pursuant to a single showing of probable cause. Prompt execution is also avoided. During such a long and continuous (24 hours a day) period the conversations of any and all persons coming into the area covered by the device will be seized indiscriminately and without regard to their connection with the crime under investigation. Moreover, the statute permits extensions of the original two-month period – presumably for two months each—on a mere showing that such extension is ‘in the public interest.’ Third, the statute places no termination date on the eavesdrop once the conversation sought is seized. Finally, the statute’s procedure, necessarily because its success depends on secrecy, has no requirement for notice as do conventional warrants, nor does it overcome this defect by requiring some showing of special facts. On the contrary, it permits unconsented entry without any showing of exigent circumstances. Such a showing of exigency, in order to avoid notice, would appear more important in eavesdropping, with its inherent dangers, than that required when conventional procedures of search and seizure are utilized. Nor does the statute provide for a return on the warrant thereby leaving full discretion in the officer as to the use of seized conversations of innocent as well as guilty parties. In short, the statute’s blanket grant of permission to eavesdrop is without adequate judicial supervision or protective procedures.61

Current Fourth Amendment Doctrine

In United States v. Jones,62 the Court seemed to revitalize the significance of governmental trespass in determining whether a Fourth Amendment search has occurred. In Jones, the Court considered whether the attachment of a Global-Positioning-System (GPS) device to a car used by a suspected narcotics dealer and the monitoring of such device for twenty-eight days, constituted a search. Although the Court ruled unanimously that this month-long monitoring violated Jones’s rights, it splintered on the reasoning. A majority of the Court relied on the theory of common law trespass to find that the attachment of the device to the car represented a physical intrusion into Jones’s constitutionally protected effect or private property.63While this holding obviated the need to assess the month-long tracking under Katz’s reasonable expectation of privacy test, five Justices, who concurred either with the majority opinion or concurred with the judgment, would have held that long-term GPS tracking can implicate an individual’s expectation of privacy.63 Some have read these concurrences as partly premised on the idea that while government access to a small data set—for example, one trip in a vehicle—might not violate one’s expectation of privacy, aggregating a month’s worth of personal data allows the government to create a mosaic about an individual’s personal life that violates that individual’s reasonable expectation of privacy.64

The Court confirmed in Carpenter v. United States that the Fourth Amendment is implicated when government action violates individuals' reasonable expectation of privacy in the whole of their physical movements, regardless of whether the challenged conduct constitutes a physical trespass.65 The Court held that the government could not, without a warrant, access seven days of a defendant's cell-site location information, which is data that continuously tracks the location of a cell phone.66 Observing that historical cell-site records present even greater privacy concerns than the GPS monitoring of a vehicle we considered in Jones, the Court highlighted the continuing importance of the expectations-of-privacy test.67The Court acknowledged that it had previously declined to extend Fourth Amendment protection to information that a person had voluntarily given to a third party like a wireless carrier, but declined to extend that line of cases to the qualitatively different category of cell-site records.68

More on the Fourth Amendment


1.    331 U.S. 145 (1947).

2.    Trupiano v. United States, 334 U.S. 699, 705 (1948)See also McDonald v. United States, 335 U.S. 451 (1948).

3.    United States v. Rabinowitz, 339 U.S. 56, 66 (1950).

4.    Chimel v. California, 395 U.S. 752, 761 (1969).

5.    Terry v. Ohio, 392 U.S. 1, 20 (1968). In United States v. United States District Court, 407 U.S. 297, 321 (1972), Justice Powell explained that the very heart of the Amendment’s mandate is that where practical, a governmental search and seizure should represent both the efforts of the officer to gather evidence of wrongful acts and the judgment of the magistrate that the collected evidence is sufficient to justify invasion of a citizen’s private premises or conversation. Thus, what is reasonable in terms of a search and seizure derives content and meaning through reference to the warrant clause. Coolidge v. New Hampshire, 403 U.S. 443, 473–84 (1971)See also Davis v. Mississippi, 394 U.S. 721, 728 (1969)Katz v. United States, 389 U.S. 347, 356–58 (1967)Warden v. Hayden, 387 U.S. 294, 299 (1967).

6.    Chimel v. California, 395 U.S. 752, 762–64 (1969) (limiting scope of search incident to arrest). See also United States v. United States District Court, 407 U.S. 297 (1972) (rejecting argument that it was reasonable to allow President through Attorney General to authorize warrantless electronic surveillance of persons thought to be endangering the national security); Katz v. United States, 389 U.S. 347 (1967) (although officers acted with great self-restraint and reasonably in engaging in electronic seizures of conversations from a telephone booth, a magistrate’s antecedent judgment was required); Preston v. United States, 376 U.S. 364 (1964) (warrantless search of seized automobile not justified because not within rationale of exceptions to warrant clause). There were exceptions, e.g.Cooper v. California, 386 U.S. 58 (1967) (warrantless search of impounded car was reasonable); United States v. Harris, 390 U.S. 234 (1968) (warrantless inventory search of automobile).

7.    See, e.g.Almeida-Sanchez v. United States, 413 U.S. 266 (1973), Justices Stewart, Douglas, Brennan, and Marshall adhered to the warrant-based rule, while Justices White, Blackmun, and Rehnquist, and Chief Justice Burger placed greater emphasis upon the question of reasonableness without necessary regard to the warrant requirement. Id. at 285. Justice Powell generally agreed with the former group of Justices, id. at 275 (concurring).

8.    E.g.G.M. Leasing Corp. v. United States, 429 U.S. 338, 352–53 (1977) (unanimous); Marshall v. Barlow’s, Inc., 436 U.S. 307, 312 (1978)Michigan v. Tyler, 436 U.S. 499, 506 (1978)Mincey v. Arizona, 437 U.S. 385, 390 (1978) (unanimous); Arkansas v. Sanders, 442 U.S. 753 (1979)United States v. Ross, 456 U.S. 798, 824–25 (1982).

9.    E.g.Chambers v. Maroney, 399 U.S. 42 (1970) (warrantless search of automobile taken to police station); Texas v. White, 423 U.S. 67 (1975) (same); New York v. Belton, 453 U.S. 454 (1981) (search of vehicle incident to arrest); United States v. Ross, 456 U.S. 798 (1982) (automobile search at scene); Brigham City, Utah v. Stuart, 547 U.S. 398 (2006) (warrantless entry into a home when police have an objectively reasonable basis for believing that an occupant is seriously injured or imminently threatened with such injury); Michigan v. Fisher, 558 U.S. ___, No. 09-91 (2009) (applying Brigham City). On the other hand, the warrant-based standard did preclude a number of warrantless searches. E.g.Almeida-Sanchez v. United States, 413 U.S. 266 (1973) (warrantless stop and search of auto by roving patrol near border); Marshall v. Barlow’s, Inc., 436 U.S. 307 (1978) (warrantless administrative inspection of business premises); Mincey v. Arizona, 437 U.S. 385 (1978) (warrantless search of home that was homicide scene); Arizona v. Gant, 556 U.S. ___, No. 07-542 (2009) (search of vehicle incident to arrest where arrestee had no access to vehicle).

10. Of the Justices on the Court in 1992, only Justice Stevens frequently sided with the warrants-with-narrow-exceptions approach. See, e.g.Illinois v. Rodriguez, 497 U.S. 177, 189 (1990) (Justice Stevens joining Justice Marshall’s dissent); New Jersey v. T.L.O., 469 U.S. 325, 370 (1985) (Justice Stevens dissenting); California v. Acevedo, 500 U.S. 565, 585 (1991) (Justice Stevens dissenting).

11. See various headings infra under the general heading Valid Searches and Seizures Without Warrants.

12. New York v. Burger, 482 U.S. 691 (1987).

13. Maryland v. Buie, 494 U.S. 325 (1990).

14. See Missouri v. McNeely, 569 U.S. 141, 156 (2013) (rejecting a per se exception to the warrant requirement for BAC blood testing in suspected drunk-driving cases and requiring that exigent circumstances be evaluated under a totality of the circumstances test). Cf. Mitchell v. Wisconsin, 139 S. Ct. 2525, 2534–35 (2019) (plurality opinion) (declining to revisit the rule established in McNeely but concluding that in circumstances involving unconscious drivers, where a breath test for BAC cannot be performed, exigent circumstances generally exist to take a warrantless blood test).

15. Illinois v. Rodriguez, 497 U.S. 177 (1990).

16. Kentucky v. King,563 U.S. 452 (2011) (police justified in entering apartment after smelling burning marijuana in a hallway, knocking on apartment door, and hearing noises consistent with evidence being destroyed).

17. United States v. Vertigo-Urquidez, 494 U.S. 259, 265 (1990).

18. See, e.g.California v. Hodari D., 499 U.S. 621, 626 (1991) (because there was no seizure of the defendant as he fled from police before being tackled, the drugs that he abandoned in flight could not be excluded as the fruits of an unreasonable seizure).

19. 19 Howell’s State Trials 1029, 1035, 95 Eng. Reg. 807, 817–18 (1765).

20. Boyd v. United States, 116 U.S. 616, 627 (1886)Adams v. New York, 192 U.S. 585, 598 (1904).

21. Thus, the rule that mere evidence could not be seized but rather only the fruits of crime, its instrumentalities, or contraband, turned upon the question of the right of the public to possess the materials or the police power to make possession by the possessor unlawful. Gouled v. United States, 255 U.S. 298 (1921)overruled by Warden v. Hayden, 387 U.S. 294 (1967)See also Davis v. United States, 328 U.S. 582 (1946). Standing to contest unlawful searches and seizures was based upon property interests, United States v. Jeffers, 342 U.S. 48 (1951)Jones v. United States, 362 U.S. 257 (1960), as well as decision upon the validity of a consent to search. Chapman v. United States, 365 U.S. 610 (1961)Stoner v. California, 376 U.S. 483 (1964)Frazier v. Cupp, 394 U.S. 731, 740 (1969).

22. 277 U.S. 438 (1928). See also Goldman v. United States, 316 U.S. 129 (1942) (detectaphone placed against wall of adjoining room; no search and seizure).

23. Silverman v. United States, 365 U.S. 505 (1961) (spike mike pushed through a party wall until it hit a heating duct).

24. Olmstead v. United States, 277 U.S. 438 (1928).

25. Among the dissenters were Justice Holmes, who characterized illegal wiretapping as dirty business, 277 U.S. at 470, and Justice Brandeis, who contributed to his opinion the famous peroration about government as the potent, the omnipresent, teacher which breeds contempt for law among the people by its example. Id. at 485. More relevant here was his lengthy argument rejecting the premises of the majority, an argument which later became the law of the land. (1) To protect [the right to be left alone], every unjustifiable intrusion by the Government upon the privacy of the individual, whatever the means employed, must be deemed a violation of the Fourth Amendment. Id. at 478. (2) There is, in essence, no difference between the sealed letter and the private telephone message. . . . The evil incident to invasion of the privacy of the telephone is far greater than that involved in tampering with the mails. Whenever a telephone line is tapped, the privacy of the persons at both ends of the line is invaded and all conversations between them upon any subject . . . may be overheard. Id. at 475–76.

26. Ch. 652, 48 Stat. 1103 (1934), providing, inter alia, that . . . no person not being authorized by the sender shall intercept any communication and divulge or publish the existence, contents, purport, effect, or meaning of such intercepted communication to any person. Nothing in the legislative history indicated what Congress had in mind in including this language. The section, which appeared at 47 U.S.C. § 605, was rewritten by Title III of the Omnibus Crime Act of 1968, 82 Stat. 22, § 803, so that the regulation of the interception of wire or oral communications in the future is to be governed by the provisions of Title III. S. Rep. No. 1097, 90th Cong., 2d Sess. 107–08 (1968).

27. 302 U.S. 379 (1937). Derivative evidence, that is, evidence discovered as a result of information obtained through a wiretap, was similarly inadmissible, Nardone v. United States, 308 U.S. 338 (1939), although the testimony of witnesses might be obtained through the exploitation of wiretap information. Goldstein v. United States, 316 U.S. 114 (1942). Eavesdropping on a conversation on an extension telephone with the consent of one of the parties did not violate the statute. Rathbun v. United States, 355 U.S. 107 (1957).

28. Weiss v. United States, 308 U.S. 321 (1939).

29. Schwartz v. Texas, 344 U.S. 199 (1952). At this time, evidence obtained in violation of the Fourth Amendment could be admitted in state courts. Wolf v. Colorado, 338 U.S. 25 (1949). Although Wolf was overruled by Mapp v. Ohio, 367 U.S. 643 (1961), it was some seven years later and after wiretapping itself had been made subject to the Fourth Amendment that Schwartz was overruled in Lee v. Florida, 392 U.S. 378 (1968).

30. Benanti v. United States, 355 U.S. 96 (1957).

31. 316 U.S. 129 (1942).

32. Silverman v. United States, 365 U.S. 505 (1961)See also Clinton v. Virginia, 377 U.S. 158 (1964) (physical trespass found with regard to amplifying device stuck in a partition wall with a thumb tack).

33. Warden v. Hayden, 387 U.S. 294, 304 (1967).

34. Katz v. United States, 389 U.S. 347, 353 (1967) (warrantless use of listening and recording device placed on outside of phone booth violates Fourth Amendment). See also Kyllo v. United States, 533 U.S. 27, 32–33 (2001) (holding presumptively unreasonable the warrantless use of a thermal imaging device to detect activity within a home by measuring heat outside the home, and noting that a contrary holding would permit developments in police technology to erode the privacy guaranteed by the Fourth Amendment.

35. 389 U.S. at 353. Justice Harlan, concurring, formulated a two pronged test for determining whether the privacy interest is paramount: 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.’ Id. at 361.

36. 389 U.S. at 351–52.

37. Mancusi v. DeForte, 392 U.S. 364, 368 (1968) (official had a reasonable expectation of privacy in an office he shared with others, although he owned neither the premises nor the papers seized). Minnesota v. Olson, 495 U.S. 91 (1990) (overnight guest in home has a reasonable expectation of privacy). But cf. Minnesota v. Carter, 525 U.S. 83 (1998) (a person present in someone else’s apartment for only a few hours for the purpose of bagging cocaine for later sale has no legitimate expectation of privacy); Cf. Rakas v. Illinois, 439 U.S. 128 (1978) (auto passengers demonstrated no legitimate expectation of privacy in glove compartment or under seat of auto). Property rights are still protected by the Amendment, however. A seizure of property can occur when there is some meaningful interference with an individual’s possessory interests in that property, and regardless of whether there is any interference with the individual’s privacy interest. Soldal v. Cook County, 506 U.S. 56 (1992) (a seizure occurred when sheriff’s deputies assisted in the disconnection and removal of a mobile home in the course of an eviction from a mobile home park). The reasonableness of a seizure, however, is an additional issue that may still hinge on privacy interests. United States v. Jacobsen, 466 U.S. 109, 120–21 (1984) (DEA agents reasonably seized package for examination after private mail carrier had opened the damaged package for inspection, discovered presence of contraband, and informed agents).

38. 533 U.S. 27 (2001).

39. 533 U.S. at 34.

40. Carpenter v. United States, 138 U.S. 2206, 2214 (2018).

41. Id. (quoting Boyd v. United States, 116 U.S. 616, 630 (1886)).

42. Id. (quoting United States v. Di Re, 332 U.S. 581, 595 (1948)).

43. Justice Harlan’s opinion has been much relied upon. See, e.g.Terry v. Ohio, 392 U.S. 1, 19 (1968)Rakas v. Illinois, 439 U.S. 128, 143–144 n.12 (1978)Smith v. Maryland, 442 U.S. 735, 740–41 (1979)United States v. Salvucci, 448 U.S. 83, 91–92 (1980)Rawlings v. Kentucky, 448 U.S. 98, 105–06 (1980)Bond v. United States, 529 U.S. 334, 338 (2000).

44. United States v. White, 401 U.S. 745, 786 (1971)See Smith v. Maryland, 442 U.S. 735, 740 n.5 (1979) (government could not condition subjective expectations by, say, announcing that henceforth all homes would be subject to warrantless entry, and thus destroy the legitimate expectation of privacy).

45. Rakas v. Illinois, 439 U.S. 128, 144 n.12 (1978).

46. E.g.Alderman v. United States, 394 U.S. 165 (1968)Mincey v. Arizona, 437 U.S. 385 (1978)Payton v. New York, 445 U.S. 573 (1980)Kyllo v. United States, 533 U.S. 27, 31 (2001).

47. E.g.United States v. Ross, 456 U.S. 798 (1982)See also Donovan v. Dewey, 452 U.S. 594 (1981) (commercial premises); Maryland v. Macon, 472 U.S. 463 (1985) (no legitimate expectation of privacy in denying to undercover officers allegedly obscene materials offered to public in bookstore).

48. E.g.United States v. Chadwick, 433 U.S. 1, 11 (1977)Katz v. United States, 389 U.S. 347, 352 (1967)But cf. South Dakota v. Opperman, 428 U.S. 364 (1976) (no legitimate expectation of privacy in automobile left with doors locked and windows rolled up). In Rawlings v. Kentucky, 448 U.S. 98 (1980), the fact that defendant had dumped a cache of drugs into his companion’s purse, having known her for only a few days and knowing others had access to the purse, was taken to establish that he had no legitimate expectation the purse would be free from intrusion.

49. Smith v. Maryland, 442 U.S. 735, 74344 (1979)See also United States v. Miller, 425 U.S. 435, 442 (1976). Concurring in United States v. Jones, 565 U.S. 400 (2012), Justice Sotomayor questioned the continuing viability of this principle in 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. Id. at 417 (Sotomayor, J., concurring). Relying on this concurrence, the Carpenter Court recognized a limit to the third-party doctrine when it decline[d] to extend Smith and Miller to the qualitatively different category of cell-site records. Carpenter, 138 S. Ct. at 2216–17. The Court noted that this data provides an all-encompassing record of the [cell phone] holder's whereabouts, tracking nearly exactly the movements of [the cell phone's] owner and operating both prospectively and retroactively. Id. at 2217–18. Instead, the Court held that an individual maintains a legitimate expectation of privacy in the record of his physical movements as captured through cell-site location information. Id. at 2217.

50. E.g.United States v. Miller, 425 U.S. 435 (1976) (bank records); Smith v. Maryland, 442 U.S. 735 (1979) (numbers dialed from one’s telephone); Hudson v. Palmer, 468 U.S. 517 (1984) (prison cell); Illinois v. Andreas, 463 U.S. 765 (1983) (shipping container opened and inspected by customs agents and resealed and delivered to the addressee); California v. Greenwood, 486 U.S. 35 (1988) (garbage in sealed plastic bags left at curb for collection).

51. City of Ontario v. Quon, 560 U.S. 746, 759 (2010). The Court cautioned that [a] broad holding concerning employees' privacy expectations vis-a-vis employer-provided technological equipment might have implications for future cases that cannot be predicted. Id. at 760.

52. United States v. White, 401 U.S. 745, 786–87 (1971) (Justice Harlan dissenting).

53. E.g.Robbins v. California, 453 U.S. 420, 429, 433–34 (1981) (Justice Powell concurring), quoted with approval in United States v. Ross, 456 U.S. 798, 815–16 & n.21 (1982).

54. Katz v. United States, 389 U.S. 347, 351–52 (1967).

55. Terry v. Ohio, 392 U.S. 1, 19 (1968).

56. The prime example is the home, so that for entries either to search or to arrest, the Fourth Amendment has drawn a firm line at the entrance to the house. Absent exigent circumstances, that threshold may not reasonably be crossed without a warrant. Payton v. New York, 445 U.S. 573, 590 (1980)Steagald v. United States, 451 U.S. 204, 212 (1981)Kirk v. Louisiana, 536 U.S. 635 (2002) (per curiam). See also Mincey v. Arizona, 437 U.S. 385 (1978). Privacy in the home is not limited to intimate matters. In the home all details are intimate details, because the entire area is held safe fromg prying government eyes. Kyllo v. United States, 533 U.S. 27, 37 (2001).

57. One has a diminished expectation of privacy in automobiles. Arkansas v. Sanders, 442 U.S. 753, 761 (1979) (collecting cases); United States v. Ross, 456 U.S. 798, 804–09 (1982). A person’s expectation of privacy in personal luggage and other closed containers is substantially greater than in an automobile, United States v. Chadwick, 433 U.S. 1, 13 (1977)Arkansas v. Sanders, 442 U.S. 753 (1979), although, if the luggage or container is found in an automobile as to which there exists probable cause to search, the legitimate expectancy diminishes accordingly. United States v. Rosssupra. There is also a diminished expectation of privacy in a mobile home parked in a parking lot and licensed for vehicular travel. California v. Carney, 471 U.S. 386 (1985) (leaving open the question of whether the automobile exception also applies to a mobile home being used as a residence and not adapted for immediate vehicular use).

58. E.g.Texas v. White, 423 U.S. 67 (1975) (if probable cause to search automobile existed at scene, it can be removed to station and searched without warrant); United States v. Robinson, 414 U.S. 218 (1973) (once an arrest has been validly made, search pursuant thereto is so minimally intrusive in addition that scope of search is not limited by necessity of security of officer); United States v. Edwards, 415 U.S. 800 (1974) (incarcerated suspect; officers need no warrant to take his clothes for test because little additional intrusion). But see Ybarra v. Illinois, 444 U.S. 85 (1979) (officers on premises to execute search warrant of premises may not without more search persons found on premises).

59. 388 U.S. 41 (1967).

60. 388 U.S. at 50–53.

61. 388 U.S. at 58–60. Justice Stewart concurred because he thought that the affidavits in this case had not been sufficient to show probable cause, but he thought the statute constitutional in compliance with the Fourth Amendment. Id. at 68. Justice Black dissented, arguing that the Fourth Amendment was not applicable to electronic eavesdropping but that in any event the search authorized by the statute was reasonable. Id. at 70. Justice Harlan dissented, arguing that the statute with its judicial gloss was in compliance with the Fourth Amendment. Id. at 89. Justice White thought both the statute and its application in this case were constitutional. Id. at 107.

62. Id. at 403–07. The physical trespass analysis was reprised in subsequent opinions. In its 2013 decision in Florida v. Jardines, the Court assessed whether a law enforcement officer had the legal authority to conduct a drug sniff with a trained canine on the front porch of a suspect’s home. Reviewing the law of trespass, the Court observed that visitors to a home, including the police, must have either explicit or implicit authority from the homeowner to enter upon and engage in various activities in the curtilage (i.e., the area immediately surrounding the home). Finding that the use of the dog to find incriminating evidence exceeded background social norms of what a visitor is normally permitted to do on another’s property, the Court held that the drug sniff constituted a search. 569 U.S. 1, 7–10 (2013). Similarly, in its 2015 per curiam opinion in Grady v. North Carolina, the Court emphasized the physical intru[sion] on a person when it found that attaching a device to a person’s body, without consent, for the purpose of tracking the person’s movements, constitutes a search within the meaning of the Fourth Amendment. 135 S. Ct. 1368, 1371 (2015). Neither the majority in Jardines nor the Court in Grady addressed whether the challenged conduct violates a reasonable expectation of privacy under Katz v. United StatesGrady, 135 S. Ct. at 1371; Jardines, 569 U.S. at 10–12.

63. Jones, 565 U.S. at 400, 431 (Alito, J., concurring in the judgment, joined by Ginsburg, Breyer, Kagan, JJ.) (concluding that respondent’s reasonable expectations of privacy were violated by the long-term monitoring of the movements of the respondent’s vehicle); id. at 415 (Sotomayor, J., concurring) (disagreeing with Justice Alito’s approach to the specific case but agreeing longer term GPS monitoring in investigations of most offenses impinges on expectations of privacy.).

64. See, e.g., In re Application for Telephone Information Needed for a Criminal Investigation, 119 F. Supp. 3d 1011, 1021–22 (N.D. Cal. 2015) (discussing the import of the two concurring opinions from Jones); United States v. Brooks, 911 F. Supp. 2d 836, 842 (D. Ariz. 2012) (noting that [w]hile it does appear that in some future case, a five justice ‘majority’ is willing to accept the principle that Government surveillance can implicate an individual’s reasonable expectation of privacy over time, Jones does not dictate the result of the case at hand . . .); but see United States v. Graham, 824 F.3d 421, 435–36 (4th Cir. 2016) (arguing that Justice Alito’s Jones concurrence should be read more narrowly so as to not implicate government access to information collected by third-party actors, no matter the quantity of information collected); In re Application of FBI, No. BR 14–01, 2014 WL 5463097, at *10 (FISA Ct. Mar. 20, 2014) (While the concurring opinions in Jones may signal that some or even most of the Justices are ready to revisit certain settled Fourth Amendment principles, the decision in Jones itself breaks no new ground . . .).

65. 138 S. Ct. 2206, 2217 (2018).

66. Id. at 2216–17.

67. Id. at 2218.

68. Id. at 2216–17.


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