The Fourth Amendment to the U.S. Constitution states 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, 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.’’ As construed by the U.S. Supreme Court, this language means that if a government action is considered a ‘‘search’’ or a ‘‘seizure,’’ it must either be authorized by a warrant issued by a magistrate, or—in emergency situations or for lesser intrusions—there must be some other reasonable justification for the action. However, if the government’s action is not a search or a seizure, then the Fourth Amendment is not implicated. Thus, the definition of these two words is crucial in determining the limitations on government efforts to investigate crime and other activities. This entry discusses the definition of search and the rules that govern searches.
To the average person, a search is an attempt to find something. But the Supreme Court has never adopted this simple definition of the term in the Fourth Amendment setting. Instead, it has looked to property and privacy concepts in establishing the threshold for constitutional restrictions on government efforts to obtain information about its citizenry.
For some time, the Court relied on property law to determine whether a police action was a search. In Olmstead v. United States, (1928), for instance, the Court held that no search occurred when federal agents eavesdropped on a conversation using a tap of telephone wires, because the tap was located outside the premises of the defendants. Similarly, in Goldman v. United States, (1942), the Court held that the Fourth Amendment was not implicated when police used a ‘‘detectaphone’’ placed against an office wall to hear private conversations. In neither case was there a physical trespass on the defendants’ privacy. Conversely, in Silverman v. United States, (1961), the Court held that electronic bugging carried out with a ‘‘spike mike’’ inserted under the baseboard of a wall until it made contact with a heating duct running throughout the defendant’s house was a search, requiring a warrant. Even physical intrusion was not a search, however, if the defendant consented to it. Thus, in On Lee v. United States, (1952), police did not conduct a search when they overheard conversations through a ‘‘bug’’ concealed on an undercover agent, because even though the agent was on the defendant’s property at the time of the overheard conversation, he was there by invitation and no trespass occurred.
Most cases involving traditional, nontechnological police intrusions do involve trespass. Thus, police entry into homes, automobiles, and luggage was considered a Fourth Amendment search under the property-based approach. However, in Hester v. United States, (1924), police trespass on private property beyond the ‘‘curtilage’’ of the home was held not to be a search, because such ‘‘open fields’’ are not a ‘‘person, house, paper or effect’’ explicitly mentioned in the Fourth Amendment and thus are not a ‘‘constitutionally protected area.’’ On the other hand, business premises, which are also not mentioned in the Fourth Amendment, did receive its protections, apparently because they are analogous to homes.
Katz v. United States, (1967) seemed to change dramatically the Supreme Court’s approach to the Fourth Amendment. In that case, police used electronic means to eavesdrop on a phone call made from a phone booth. The government argued that this surveillance did not constitute a Fourth Amendment search both because a phone booth is not a ‘‘constitutionally protected area’’ identified in the Fourth Amendment and because the bugging device did not physically intrude into the booth. Based on precedent, these arguments should have won. But the Court stated that the Fourth Amendment ‘‘protects people, not places,’’ and found that Katz deserved its protections once he closed the door to the booth and excluded the uninvited ear. In a concurring opinion, Justice Harlan noted that, although the Fourth Amendment protects people, explaining how it does so will usually require reference to a place. Rather than using property law to describe which places are protected, however, Harlan suggested that a search should be said to occur when police infringe ‘‘expectations of privacy that society is prepared to recognize as reasonable.’’ It was this ‘‘reasonable expectation of privacy’’ language that the Court subsequently came to use in defining ‘‘search’’ for Fourth Amendment purposes.
Although the result in Katz suggested that the decision would broaden the scope of the Fourth Amendment beyond the constraints imposed by property law, in fact most of the Court’s post-Katz decisions are fully consistent with the Court’s earlier jurisprudence. Both Hester and On Lee have been affirmed since Katz, the first holding on the ground that people do not have a reasonable expectation of privacy in private property that is not adjacent to the home and the second because they assume the risk their acquaintances work for the police. The assumption- of-risk rationale was expanded in Smith v. Maryland, (1979), which held that people have no reasonable expectation of privacy in the phone numbers they dial (because they know or should know the phone company records these numbers and may hand them over to authorities) and in United States v. Miller, (1976), which held that no search occurs when prosecutors subpoena information disclosed to a bank (because the ‘‘depositor takes the risk, in revealing his affairs to another, that the information will be conveyed by that person to the government’’). Nor does a search occur when police use a dog to sniff luggage, an airplane to spy on a backyard or business cartilage, or an electronic beeper to trace the whereabouts of a car. Furthermore, police do not have to be concerned about the Fourth Amendment when they go through garbage left at curbside or look inside a barn from open fields. Probably none of these actions would have been searches under a trespass analysis either, but the point is that Katz changed nothing in these settings.
A few cases suggest that the expectation-of-privacy rubric is somewhat more expansive than propertybased analysis. In Bond v. United States, (2000), the Court held that police engaged in a Fourth Amendment search when they tried to discern the contents of a soft bag by feeling its contours. Although no physical intrusion occurred and the bag was not moved, the touching of the bag made the police action a search. Similarly, in Kyllo v. United States, (2001), the Court concluded that use of a thermal imaging device to detect heat differentials inside a home was a search, even though no physical intrusion occurred and the police using the device were stationed on public property. However, the Kyllo opinion also indicated that if the spying of the home interior from a lawful vantage point had been with the naked eye, with a technological device that merely replicated what the naked eye could have seen, or with a technological device that is in ‘‘general public use’’ (a flashlight or binoculars), then no search would have occurred. Thus, even in connection with the most private enclave, the home, the Court’s assessment of ‘‘reasonable expectations of privacy’’ narrowly defines the privacy we can expect from government intrusion.
A reading of the Supreme Court’s cases and lower court cases applying the expectations of privacy test suggests seven factors that might be relevant in deciding whether a search has occurred: (1) the nature of the place observed (for example, a home v. a public park); (2) the steps taken to enhance privacy (for example, a curtained window v. an open porch a few feet from the street); (3) the degree to which the surveillance requires a physical intrusion onto private property (for example, viewing from a tree in the fenced-in backyard of a house v. viewing from the sidewalk); (4) the nature of the object or activity observed (for example, a conversation v. contraband or outdoor piping); (5) the degree to which any technology used to view the premises is available to the general public (for example, satellite photography v. a flashlight); (6) the extent to which any technology used ‘‘replaces’’ rather than merely ‘‘improves’’ the senses (for example, a device that can see through clothes v. binoculars); and (7) the extent to which the viewing is unnecessarily pervasive, invasive, or disruptive (for example, surveillance of hundreds of people v. surveillance of one person; week-long surveillance v. a brief viewing). Note that many of these factors, especially (2), (3), and (5), make it less likely poor people, who have fewer means of protecting their privacy, will benefit from the Fourth Amendment.
Because it establishes when the government must abide by the Fourth Amendment, the definition of search is a major determinant of the type of society in which we live. Many commentators disagree with both the property and the privacy approaches to that definition, at least as applied by the Supreme Court. One suggested alternative is to define search in terms of the ‘‘positive law,’’ that is, the law governing relationships between private citizens. That law includes not only the rules of trespass but also the tort and regulatory rules governing third-party access to bank records, phone numbers, garbage, and the like. Another suggested alternative is to base the scope of ‘‘expectations of privacy society is prepared to recognize as reasonable’’ on an empirical assessment of the expectations society actually has. Preliminary research in this vein indicates, not surprisingly, that most people do not expect acquaintances, banks, or phone companies to be government agents, and that most people think that investigative techniques such as binocular surveillance of homes and beeper tracking of cars is much more intrusive than the Court does. A third alternative is to base the definition of search on historical information about what the Framers of the Constitution considered intrusive. Each of these approaches has problems. Positive law may be over or under inclusive (compare laws making any presence on private property a trespass to the absence of laws governing spying into backyards), society’s views can be hard to discern and may be variable, and historical attitudes, even if they can be ascertained, may not have anything to say about modernday surveillance.
A final approach is to define search as a layperson would: an attempt to find evidence of crime. The main reason the Court has avoided this simple definition is that, once a government action is labeled a search, precedent has usually required that the police have probable cause, a level of certainty akin to a morelikely- than-not finding. Because police look for evidence of crime not only in houses but also in public and quasipublic places, the ‘‘lay definition’’ of search, combined with the probable cause requirement, would severely hamper law enforcement. If, however, the Court were willing to permit less intrusive searches on less than probable cause (and permit the least intrusive searches on little or no suspicion), that tension would be mitigated considerably. However, as discussed later, the Court has been unwilling to adopt this ‘‘proportionality’’ approach to Fourth Amendment jurisprudence.
As just noted, if a government action is a search, police usually must have probable cause to believe that evidence will be discovered in the place searched. Following is a more detailed summary of the rules governing searches, organized in terms of the Fourth Amendment’s ‘‘persons, houses, papers and effects.’’
Searches of persons generally require probable cause, but there are several exceptions. A search of a person incident to arrest requires probable cause for the arrest but no independent suspicion for the search. A frisk, or patdown, that occurs after a stop (which is a brief detention short of an arrest) may be based on reasonable suspicion, a standard that requires articulable grounds but not at the probable cause level (Terry v. Ohio, 1968). Finally, an inventory search of an individual who has been arrested requires no suspicion as long as it is pursuant to a written inventory policy.
If the search is of a house or a private business, police must usually have a warrant, unless there are exigent circumstances. Such circumstances exist when police are in hot pursuit of a felon, when police have arrested a person inside the home or business and want to check the arrestee’s immediate surroundings for confederates, or when they have reasonable suspicion that a confederate is hiding somewhere else in the vicinity. If the search of the house or business is an administrative inspection (for example, a health or safety inspection), then the probable cause for the warrant need not be ‘‘individualized’’ but can consist of a showing that the structure is in an area or involved in a type of industry that is due for inspection. Furthermore, warrants are never needed to inspect ‘‘pervasively regulated industries’’ on the theory that owners of such enterprises are on notice they will be subject to search.
At one time searches of papers were prohibited unless they were considered instrumentalities of crime (that is, they were instrumental in carrying out the crime—accounts of bookmaking—rather than ‘‘mere evidence’’ of it). Today, virtually all papers, except perhaps private diaries and the like, may be searched in one of two ways. First, the government may proceed pursuant to a subpoena based on a finding that the papers are ‘‘relevant’’ to a criminal investigation (a level of certainty lower than both probable cause and reasonable suspicion). Second, the government may seek the papers pursuant to a warrant based on probable cause, a method likely to be used when police are concerned the possessor of the papers is likely to destroy them rather than respond to a subpoena, or where the fact that the papers exist is incriminating and thus compelling their production through a subpoena would violate the Fifth Amendment (see Fisher v. United States, 1976).
Finally, effects, or personal property, such as cars, luggage, clothing, and the like, can be searched if there is probable cause. If these items are in a house, they need to be listed in a warrant, found in a place where items listed in the warrant may be found, or found in plain view while a valid warrantless search is being carried out. With respect to searches of cars and other moveable vehicles, no warrant is required. But probable cause is, unless the occupants of the car have been arrested or police have reasonable suspicion that the occupants can reach a weapon in the car. Furthermore, if a car is lawfully impounded (because, for example, the occupants have been arrested or there are outstanding parking tickets), it may be inventoried under a written inventory policy.
Standing doctrine determines when a particular defendant can assert a Fourth Amendment claim. It is related to the definition of search because a criminal defendant’s standing to contest a given police action depends on whether it infringes the defendant’s own legitimate expectations of privacy. Thus, the Supreme Court has held that a defendant cannot challenge the government’s burglarization of a third party’s apartment and briefcase, even though the evidence discovered was used against the defendant, because the defendant had no expectation of privacy in the third party’s premises or effects. Similarly, the Court held that defendants could not challenge the search of a car that produced bullets and a gun subsequently used against them in court, because they neither owned nor were driving the car at the time of the search.
References and Further Reading
Cases and Statutes Cited
See also Amsterdam, Anthony G.; Carroll v. United States, 267 U.S. 132 (1925); Coolidge v. New Hampshire, 403 U.S. 443 (1971); Drug Testing; Electronic Surveillance, Technological Monitoring, and Dog Sniffs; Exclusionary Rule; Fisher v. United States, 425 U.S. 391 (1976); Florida v. Riley, 488 U.S. 445 (1989); Hester v. United States, 265 U.S. 57 (1924); Hoffa v. United States, 385 U.S. 293 (1966); Katz v. United States, 389 U.S. 347 (1967); Kyllo v. United States, 533 U.S. 27 (2001); Olmstead v. United States, 277 U.S. 438 (1928); Open Fields; Privacy; Probable Cause; Search Warrants; Seizures; Terry v. Ohio, 392 U.S. 1 (1968); United States v. Miller, 425 U.S. 435 (1976); Warrantless Searches