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The Fourth Amendment to the U.S. Constitution provides 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 . . . constitutional prohibition against unreasonable searches and seizures, has its source in that principle of the common law which finds expression in the maxim that 'every man's house is his castle.' English history discloses [that the] . . . constitutional provisions . . . had their origin 'in the . . . unwarrantable intrusion of executive agents into the houses . . . of individuals . . . .'"[1]

This right had a long history in English common law. Sometimes colloquially expressed as “a man’s house is his castle,” it meant that one had a right to expect that one’s home, possessions, and person were safe against arbitrary and forceful intrusion by the King’s agents. At the same time, it recognized that the lawful agents of the state can intrude on private property to execute or enforce the law, so long as they obey certain procedural rules that protect the subject of the search.

This protection was understood in 1787 to limit and regulate physical trespass, and the seizing of papers, effects, or "things." However, it gradually came to be seen as a protection of something more.[2] "[T]he principal object of the Fourth Amendment," the U.S. Supreme Court has explained, "is the protection of privacy rather than property.”[3] In addition, "the Fourth Amendment protects people — and not simply 'areas' — against unreasonable searches and seizures."[4] Thus, in its seminal decision in Katz v. United States,[5] the Court held that police officers violated the Fourth Amendment when they conducted a warrantless search using a listening and recording device placed on the outside of a public phone booth to eavesdrop on the conversation of a suspect who had "'justifiably relied' upon . . . [the privacy of the] telephone booth."[6] The Court concluded that the Fourth Amendment protects both a person and that person’s expectation of privacy from warrantless searches or seizures in places which are justifiably believed to be private.

The Amendment's operative text can be divided into two clauses. The first clause forbids the government from conducting any search or seizure that is "unreasonable." The second clause prohibits the government from issuing a warrant unless it is obtained based "upon probable cause," is "supported by Oath," and contains particularized descriptions of the "place to be searched" and what is "to be seized." Although "[t]here is nothing in the amendment’s text to suggest that a warrant is required to make a search or seizure reasonable,"[7] the U.S. Supreme Court has long since read these two clauses together, generally holding that a warrantless search or seizure is presumptively (if not per se) unreasonable.[8]

Searches and seizures[]

The critical triggering phrase of the fourth amendment is “searches and seizures.” If there is no search or seizure, then official behavior is not covered by the Fourth Amendment, and it need not be reasonable, based on probable cause, or carried out pursuant to a warrant. Although there may be statutory protections that require certain conduct, an individual does not have fourth amendment protections unless there is a search and seizure.

Definition of "search"[]

The U.S. Supreme Court has said that a “search” occurs where the Government infringes upon a person’s reasonable expectation of privacy, consisting of both an actual, subjective expectation of privacy as well as an objectively reasonable expectation of privacy, which requires both that an “individual manifested a subjective expectation of privacy in the searched object” and that “society is willing to recognize that expectation as reasonable.”[9] Thus, the Fourth Amendment ultimately limits the government’s ability to conduct a range of activities, such as physical searches of homes or offices and listening to phone conversations. As a general rule, the Fourth Amendment requires the government to demonstrate “probable cause” and obtain a warrant (unless a recognized warrant exception applies) before conducting a search.[10]

Definition of "seizure"[]

A “seizure” of a person occurs when a government official makes an individual reasonably believe that he or she is not at liberty to ignore the government’s presence in view of all the circumstances surrounding the incident.


The secondary triggering phrase of the fourth amendment is “unreasonable.” Even if official conduct is regarded as a search or seizure, there is no invasion of fourth amendment protections if the conduct is reasonable. Determination of reasonableness depends on the judicial balancing of the individual interest, generally regarded as a privacy interest, against the governmental interest, including law and order, national security, internal security, and the proper administration of the laws. Reasonableness generally entails a predicate of probable cause and, with many exceptions, the issuance of a warrant.

Warrant based upon probable cause[]

The U.S. Supreme Court has interpreted the Fourth Amendment to include a presumptive warrant requirement on all searches and seizures conducted by the government, and has ruled that any violations of this standard will result in the suppression of any information derived therefrom.

Generally, the same warrant rules apply when preparing and executing a search warrant for digital evidence as in other investigations. Law enforcement should consider the following when preparing and executing a search warrant for digital evidence:

1. Describing property. If the evidence sought is the computer itself (and the hardware is an instrumentality, a fruit of the crime, or contraband), then the warrant should describe the computer as the target of the search. If the evidence sought is information that may be stored on digital media, then the warrant should describe what that evidence is and request the authority to seize it in whatever form (including digital) it may be stored. This includes requesting authority to search for evidence of ownership and control of the relevant data on the media.
2. Conducting a search. In some cases, a search of an electronic storage device can require significant tech­nical knowledge and should be conducted by appropriate personnel who are sup­plied with a copy of the search warrant to ensure that the search is within its scope. In the course of conducting a search, law enforcement may discover passwords and keys that could facilitate access to the system and data. Law enforcement may also find evidence of a crime that is outside the scope of the search warrant. In such an event, law enforcement should consider securing another warrant to expand the scope of the search.
3. Reasonable accommodations. In some cases, it might be impractical to search the device on-site. If a device is to be searched off-site, law enforcement should consider adding language to the warrant affidavit that justifies its removal. If a device is removed for an off-site search, the search should be completed in a timely manner. Law enforcement may consider returning copies of noncontraband seized data, even if they are commingled with evidence of a crime, to accommodate a reasonable request from suspects or third parties.

The U.S. Supreme Court, however, has also recognized situations that render the obtainment of a warrant impractical or against the public’s interest, and has accordingly crafted various exceptions to the warrant and probable cause requirements of the Fourth Amendment.

Intelligence gathering[]

While the right against unreasonable searches and seizures was originally applied only to tangible things, Supreme Court jurisprudence eventually expanded the contours of the Fourth Amendment to cover intangible items such as conversations. However, the extent to which the Fourth Amendment warrant requirement applies to the government’s collection of information for intelligence gathering and other purposes unrelated to criminal investigations is unclear.

As communications technology has advanced, the technology for intrusion into private conversations has kept pace, as have government efforts to exploit such technology for law enforcement and intelligence purposes. At the same time, the Supreme Court has expanded its interpretation of the scope of the Fourth Amendment with respect to such techniques, and Congress has legislated both to protect privacy and to enable the government to pursue its legitimate interests in enforcing the law and gathering foreign intelligence information. Yet the precise boundaries of what the Constitution allows, as well as what it requires, are not fully demarcated, and the relevant statutes are not entirely free from ambiguity.

Although the surveillance of wire or oral communications for criminal law enforcement purposes was held to be subject to the warrant requirement of the Fourth Amendment in 1967,[11] neither the Supreme Court nor Congress sought to regulate the use of such surveillance for national security purposes at that time. Title III of the Omnibus Crime Control and Safe Streets Act of 1968 (as originally enacted), contained an exception that stated:

Nothing contained in this chapter or in section 605 of the Communications Act . . . shall limit the constitutional power of the President to take such measures as he deems necessary to protect the Nation against actual or potential attack or other hostile acts of a foreign power, to obtain foreign intelligence information deemed essential to the security of the United States, or to protect national security information against foreign intelligence activities. . . .[12]

Several years later, the Supreme Court invalidated warrantless electronic surveillance of domestic organizations for national security purposes, but indicated that its conclusion might differ if the electronic surveillance targeted foreign powers or their agents.[13] A lower court has since upheld the statutory scheme governing the gathering of foreign intelligence information against a Fourth Amendment challenge, despite an assumption that orders issued pursuant to the statute might not constitute “warrants” for Fourth Amendment purposes.[14] The Supreme Court has not yet directly addressed the issue. However, even if the warrant requirement was found not to apply to searches for foreign intelligence or national security purposes, such searches would presumably be subject to the general Fourth Amendment “reasonableness” test.[15]

Warrantless searches[]

There are several well-recognized exceptions to securing a warrant. Although the following is not an exhaustive list, the examples provide an idea of how the common exceptions apply to the search and seizure of digital evidence.

Consent. Consent is a valuable tool for an investigator. It can come from many sources, including a log-in banner, terms-of-use agreement, or company policy. Some considerations include:

(1) Like a shared apartment, a computer can have multiple users. Consent by one user is always sufficient to authorize a search of that person’s private area of the computer, and in most instances is sufficient to authorize a search of the com­mon areas as well. Additional consent may be needed if law enforcement encoun­ters password-protected files. Also, a parent in most cases can consent to a search of a minor child’s computer.
(2) Consent can be limited by subject matter, duration, and other parameters. Consent can be withdrawn at any time.
(3) The general rule is that a private-sector employer can consent to a search of an employee’s workplace computer. The rules are more complicated when the employer is the government.

Exigent circumstances. To prevent the destruction of evidence, law enforcement can seize an electronic storage device. In certain cases in which there is an immediate danger of losing data, law enforcement may perform a limited search to preserve the data in its cur­rent state. Once the exigent circumstances end, so does the exception.

Search incident to arrest. The need to protect the safety of law enforcement or to preserve evidence can jus­tify a full search of an arrestee and a limited search of the arrest scene. This search incident to arrest can include a search of an electronic storage device, such as a cell phone or pager, held by the subject.

Inventory search. The inventory search exception is intended to protect the property of a person in custody and guard against claims of damage or loss. This exception is untested in the courts, so it is uncertain whether the inventory search exception will allow law enforcement to access digital evidence without a warrant.

Plain view doctrine. The plain view doctrine may apply in some instances to the search for and seizure of digital evidence. For plain view to apply, law enforcement must legitimately be in the position to observe evidence, the incriminating character of which must be immediately apparent. Law enforcement officials should exercise caution when relying on the plain view doctrine in connection with digital media, as rules concerning the application of the doctrine vary among jurisdictions.

Documents held by third parties[]

In contrast with its rulings on surveillance, the Supreme Court has not historically applied the protections of the Fourth Amendment to documents held by third parties. In 1976, it held that financial records in the possession of third parties could be obtained by the government without a warrant.[16] Later, it likewise held that the installation and use of a pen register — a device used to capture telephone numbers dialed — does not constitute a Fourth Amendment search.[17] The reasoning was that individuals have a lesser expectation of privacy with regard to information held by third parties.

In response to the Supreme Court’s rulings regarding the Fourth Amendment’s non-application to documents held by third parties, Congress enacted the Right to Financial Privacy Act (RFPA)[18] to constrain government authorities’ access to individuals’ financial records. Although these privacy protections are subject to a foreign intelligence exception,[19] government authorities were not authorized to compel financial institutions to secretly turn over financial records until 1986.[20] That year, the FBI was also given authority, in the form of FBI-issued “national security letters,” to access customer records held by telephone companies and other communications service providers in specified instances justified by a national security rationale.[21] Two additional national security letter authorities were enacted in the mid-1990s. The first provided access to credit and financial records of federal employees with security clearances.[22] The second gave the FBI access to credit agency records in order to facilitate the identification of financial institutions utilized by the target of an investigation.[23]

Fourth Amendment analysis[]

At its broadest, a Fourth Amendment analysis is a two-stage inquiry. First, was the action of a government officer toward a person or thing sufficiently intrusive to constitute a “search” or “seizure?”[24] Second, if a “search” or “seizure” did occur, was the intrusionreasonable” in light of the circumstances? The “reasonableness” of a particular government action is judged by balancing the governmental interest which allegedly justifies the official intrusion against a person’s legitimate expectations of privacy. Courts must consider the scope of the particular intrusion, the manner in which it is conducted, the justification for initiating it, and the place in which it is conducted.

If a court determines that a government intrusion constitutes a “search” or “seizure” that was not reasonable in light of the relative weights of the government’s interest and a person’s constitutionally protected privacy interests, it will conclude that a Fourth Amendment violation has occurred. A violation of the Fourth Amendment may, as a general rule, result in the suppression of any information derived therefrom in a judicial proceeding.

Government action[]

In most circumstances, government action is implicated when a government official conducts a search. Generally speaking, the Fourth Amendment’s limitations do not apply to searches by private parties unless those searches are conducted at the direc­tion of the government. Private parties who independently acquire evidence of a crime may turn it over to law enforcement.[25]

For example, if an employee discovers contraband files on a computer that is being repaired in a shop, the employee’s subsequent release of information to law enforce­ment does not violate the Fourth Amendment. In such a case, law enforcement may examine anything that the employee observed.

Reasonable expectation of privacy[]

The Fourth Amendment applies when the searched party has an actual expectation of privacy in the place to be searched or thing to be seized, and then only if it is an expectation that society is prepared to recognize as reasonable.[26]

[F]irst 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."[27]

The subjective part of the test focuses attention on the means the individual employs to protect his or her privacy, e.g., closing the door of a phone booth or closing curtains. Additionally, the assumption of risk that the individual appears to take is considered in determining the individual’s actual expectation of privacy. Under assumption of risk, an individual is presumed to assume the risk that another party to a conversation or activity may consent to a search. This assumption of risk prevails even if the consenting party is an informer or undercover agent.[28]

The objective part of the test looks to what society regards as a reasonable expectation of privacy. Yet, it requires this without specifying an objective referent. Is “society” today’s opinion polls, longstanding norms and traditions, a reasonable person, or the knowledge that people have in common? The result of the objective part of the test is that the Court has implicitly constructed a continuum of circumstances under which society would regard an individual as having a reasonable expectation of privacy. The continuum ranges from public places (“open fields,” “in plain view,” “public highway”), in which there is no objective expectation of privacy except in unusual circumstances, to the inside of one’s home with the windows and curtains shut and the door bolted, in which there is an objective expectation of privacy. The objective expectation of privacy along the continuum (shopping centers, motels, offices, automobiles, and yards) depends on judicial interpretation. The Court has modified the objective element, referring to it as a ‘‘legitimate’ expectation of privacy."

Some courts treat a computer as a “closed container” for Fourth Amendment purposes. In some jurisdictions, looking at a computer’s subdirectories and files is akin to opening a closed container.

People, not places[]

The second important component of Katz v. United States is the holding that ‘‘the fourth amendment protects people, not places.” The question of what protection the fourth amendment offers people remains unanswered, and defining the scope of such protection still necessitates reference to places. Moreover, the distinction between “people” and “places” has raised the question of whether the fourth amendment still protects property interests, or whether it now protects only more personal interests. The issue of the protection afforded people as distinct from that afforded places has become more significant with the growth of third-party recordkeepers, e.g., banks. The thrust of the U.S. Supreme Court opinion in Katz seemed to represent an expansion, not a replacement, of the existing fourth amendment protections:

The 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.[29]

It has been argued that, based on Katz, analysis of privacy interests should replace the more traditional property analysis when the Government uses nonphysical methods of search and where relevant privacy interests do not have physical characteristics. The property aspect is viewed as still important because it gives specificity and concreteness to fourth amendment analysis. Yet, in some rulings the U.S. Supreme Court has treated privacy as the only interest protected by the fourth amendment.

This implies a further narrowing of fourth amendment protection, both because property interests are not considered and because of the problems of defining privacy. In evaluating the appropriateness of the use of electronic surveillance technologies by Government officials, the courts have worked within the framework established by Katz. By analogy to traditional surveillance devices, the courts have attempted to determine whether or not individuals have a reasonable expectation of privacy. This becomes more difficult as surveillance devices become more technologically sophisticated because the analogy is often more remote and hence less convincing. The courts have generally continued to consider the place in which a surveillance device is located or the place that a device is monitoring. The courts generally have adopted the more expansive interpretation of Katz and have not abandoned higher levels of protection for certain places, e.g., homes and yards.

Yet, the Katz framework has not offered the courts sufficient policy guidance to deal with the range and uses of new surveillance technologies. "Reasonable expectation of privacy" is an inherently nebulous phrase and, despite decades of judicial application, predicting its meaning in a new context is difficult. Determining whether a place is sufficiently private to offer protection against official surveillance is more and more difficult as the public sphere of activities encroaches on what was once deemed private.


The Fourth Amendment search and seizure provision protects a right of privacy by requiring warrants before government may invade one's internal space or by requiring that warrantless invasions be reasonable. However, "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."[30]


  1. United States v. Three Tons of Coal, 28 F. Cas. 149, 151 (E.D. Wis. 1875). See also Semayne’s Case, 5 Co. Rep. 91a, 91b, 77 Eng. Rep. 194, 195 (K.B. 1603) ("[T]he house of every one is to him as his castle and fortress.").
  2. See, e.g., Silverthorne Lumber Co. v. United States, 251 U.S. 385 (1920); Jones v. United States, 362 U.S. 257, 266 (1960), overruled on other grounds by United States v. Salvucci, 448 U.S. 83 (1980); Silverman v. United States, 365 U.S. 505, 511-12 (1961); Warden v. Hayden, 387 U.S. 294, 304 (1967); Rakas v. Illinois, 439 U.S. 128, 143 (1986).
  3. Warden, 387 U.S. at 304-05 (discussing the shift from an emphasis from property to privacy).
  4. Katz, 389 U.S. at 353. This focus finds support in the Amendment's text, which begins by stating that it protects "[t]he right of the people." U.S. Const. amend. IV.
  5. 389 U.S. 347 (1967).
  6. Kyllo, 533 U.S. at 33 (quoting Katz, 389 U.S. at 353).
  7. United States v. Garcia, 474 F.3d 994, 996 (7th Cir. 2007).
  8. See, e.g., City of Ontario v. Quon, 130 S.Ct. 2619, 2630 (2010); Brigham City v. Stuart, 547 U.S. 398, 403 (2006); Groh v. Ramirez, 540 U.S. 551, 559 (2004); United States v. Ross, 456 U.S. 798, 824-25 (1982); Mincey v. Arizona, 437 U.S. 385, 390 (1978); Katz v. United States, 389 U.S. 347, 357 (1967). The U.S. Supreme Court has gone back and forth on whether warrantless searches or ]]seizure]]s are presumptively unreasonable or per se unreasonable. It is unclear which approach the Court currently follows.
  9. Kyllo v. United States, 533 U.S. 27, 33 (2001) (citing California v. Ciraolo, 476 U.S. 207, 211 (1986)).
  10. See, e.g., Atwater v. City of Lago Vista, 532 U.S. 318, 354 (2001) (recognizing a warrant exception for arrest of an individual who commits a crime in an officer’s presence, as long as the arrest is supported by probable cause).
  11. Katz v. United States, 389 U.S. 347, 353 (1967), overruling Olmstead v. United States, 277 U.S. 438 (1928).
  12. 82 Stat. 214, formerly codified at 18 U.S.C. §2511(3).
  13. United States v. U.S. District Court, 407 U.S. 297, 313-14, 321-24 (1972) (also referred to as the Keith case, so named for the District Court judge who initially ordered disclosure of unlawful warrantless electronic surveillance to the defendants). See also In re Directives, 551 F.3d 1004, 1011 (Foreign Intell. Surveillance Ct. Rev. 2008) (holding that the foreign intelligence surveillance of targets reasonably believed to be outside of the U.S. qualifies for the “special needs” exception to the warrant requirement).
  14. In re Sealed Case, 310 F.3d 717, 738-46 (Foreign Intell. Surveillance Ct. Rev. 2002).
  15. The “general reasonableness,” or “totality-of-the circumstances,” test requires a court to determine the constitutionality of a search or seizure “by assessing, on the one hand, the degree to which [a search or seizure] intrudes upon an individual’s privacy and, on the other, the degree to which it is needed for the promotion of legitimate governmental interests.” Samson v. California, 547 U.S. 843, 848 (2006).
  16. United States v. Miller, 425 U.S. 435 (1976)
  17. Smith v. Maryland, 442 U.S. 735, 745-46 (1979).
  18. Pub. L. No. 95-630, §1114, 12 U.S.C. §3401 et seq.
  19. 12 U.S.C. §3414(a)(1)(A), (B).
  20. Pub. L. No. 99-569, §404, 12 U.S.C. §3414(a)(5)(A).
  21. Electronic Communications Privacy Act, Pub. L. No. 99-508, §201(a), 18 U.S.C. §2709.
  22. Pub. L. No. 103-359, §802, 50 U.S.C. §436.
  23. Pub. L. No. 104-93, §601(a), 15 U.S.C. §1681u.
  24. See Oliver v. United States, 466 U.S. 170, 177-78 (1984); see also Walter v. United States, 447 U.S. 649, 656 (1980) (noting that a wrongful search or seizure conducted by a private party does not violate the Fourth Amendment. . . .).
  25. Law enforcement may replicate a private search, but may not exceed the scope of that search without a warrant or exception to the warrant requirement.
  26. Katz v. United States, 389 U.S. 347, 360 (1967).
  27. Id. at 361 (Harlan, J., concurring).
  28. See the “false friends cases" — United States v. White, 401 U.S. 745 (1971), Hoffa v. United States, 385 U.S. 293 (1966); Lopez v. United States, 373 U.S. 427 (1967). In White the Court ruled that agents can be wired for sound and still be covered by the assumption of risk, reasoning that the risk did not increase materially simply because the informers were transmitting the conversation electronically. Smith v. Maryland, 442 U.S. 735 (1979) and United States v. Knotts, 460 U.S. 276 (1983) suggest that an individual forfeits his expectation of privacy by risking the possibility that his activities will be revealed to the police.
  29. Katz v. United States, 389 U.S. 347, 350 (1967).
  30. Id.


See also[]