The Fourth Amendment protects against unreasonable searches, and the Supreme Court has concluded that warrantless searches, even if probable cause is present, “are per se unreasonable” (Katz v. United States, 1967). Still, most commentators agree that searches under warrant have played a relatively minor part in law enforcement because of the number and breadth of exceptions to this requirement. Exceptions occur when it is impractical to secure a warrant or when there is explicit or implied consent to the search. Also, warrants may not be required when facts and circumstances preclude any reasonable expectation of privacy. Exceptions to the warrant rule include but are not limited to: searches incident to a lawful arrest or required to ensure safety, such as “stop and frisk” procedures; inspections by customs, border, and airport officials; searches made with the suspect's consent; searches made in compliance with lawful government actions, such as health inspections; searches of items in plain view; and searches of student belongings. The same probable cause standard applies to all searches, under warrant or not (Brinegar v. United States, 1949.)
A long‐standing exception permits warrantless searches incident to a lawful arrest. Circumstances may not permit an arresting officer to obtain a warrant. But only the person under arrest and the immediately surrounding area are subject to search (Chimel v. California, 1969), although a cursory visual inspection of adjacent hiding places may be conducted as a protective measure (Maryland v. Buie, 1990). Unusual circumstances may justify a warrantless search even though no arrest is made. These exceptions rest on the need of law officers to protect themselves and others. Courts will judge after the fact whether “exigent circumstances” justified the exception, including the officer's reasonable suspicions based on his experience, the suspect's conduct and reputation, and other relevant factors (Terry v. Ohio, 1968). Following Terry the standard became less restrictive, with the Supreme Court permitting an officer to act without probable cause upon “reasonable suspicion of criminal activity” (United States v. Hensley, 1986). Not all police actions incident to an arrest are permitted. For example, police may not conduct a warrantless search of a private home in order to make a felony arrest (Payton v. New York, 1980), nor may they search without probable cause other parties who happen to be in a place also occupied by a suspect (Ybarra v. Illinois, 1979) (see Stop and Frisk Rule).
Prior to the 1960s, administrative inspections for violations of municipal codes and other government regulations fell outside the restrictions of the Fourth Amendment. In Camara v. Municipal Court (1967), however, the Supreme Court extended warrant protection to a homeowner who refused to permit a warrantless code‐enforcement inspection of his personal residence. But in James v. Valtierra (1971), the Court held that home visitations for welfare programs did not require a warrant because, unlike a code violation, refusal subjected a person to loss of governmental support only, not criminal prosecution. The Court also has generally deferred to congressional determinations as to when a warrant is not required, such as in a warrantless search of a gun dealer's locked storeroom during business hours, an action explicitly authorized under the Gun Control Act of 1968. Heavily regulated industries, such as guns or liquor, have no reasonable expectation of privacy and thus are subject to warrantless searches.
New technology often has persuaded the Court to carve exceptions from the search warrant rule. In Carroll v. United States (1925), the justices upheld a warrantless search of an automobile used by suspected bootleggers. Probable cause existed, and there was not time to secure a warrant because the car and its illegal cargo could escape. The automobile exception still exists. Evidence from these warrantless searches is acceptable so long as there was probable cause for stopping the car, even if the evidence is concealed from view (United States v. Ross, 1982.) The interior of an automobile is not subject to the same expectation of privacy that exists in a home (New York v. Class, 1986). Also, protective searches are permitted at fixed checkpoints, such as for sobriety checks, because of the absence of individualized suspicion, but the same exception does not apply to random stops of automobiles (see Automobile Searches). Significantly, the same protections do not extend to vessels, which may be boarded and searched randomly for purposes of inspecting documentation (United States v. Villamonte‐Marquez, 1983).
Another exception, no longer applicable, appeared with wiretapping. In Olmstead v. United States (1928), the Court concluded that this new technology was only an enhanced sense of hearing, not a warrantless invasion of one's premises. The opinion brought a famous dissent from Justice Louis D. *Brandeis, who warned that the government was breaking the law by illegally invading a person's privacy, which was at the heart of the Fourth Amendment guarantee. Congress in 1934 prohibited wiretap evidence in federal courts, but not until 1967, in Berger v. New York and Katz v. United States, did the Court extend Fourth Amendment requirements to electronic surveillance, although the USA Patriot Act (2001) created new exemptions.
Other exceptions are worthy of note. Routine customs searches require no warrant or no probable cause, though extended detention of travelers must be justified by reasonable suspicion (United States v. Montoya de Hernandez, 1985). School officials, on reasonable suspicion, may search student belongings or lockers for proscribed articles, such as guns and drugs (New Jersey v. T.L.O.,1985). Similar principles apply to public employer work‐related searches of employee offices, desks, and file spaces (O'Connor v. Ortega, 1987). No warrant, probable cause, or individualized suspicion is needed for mandatory drug testing of certain classes of railroad and public employees or for random drug testing of school children. Naked‐eye aerial surveillance of a person's backyard or through the partially open roof of an outbuilding does not constitute a search, even if it reveals illegal activity that leads to a warrant and arrest (California v. Ciraolo, 1986; United States v. Riley, 1989). In Kyllo v. United States (2001), however, the Supreme Court ruled that officers could not search a home using infrared devices without first establishing probable cause.
The anti‐terrorist USA Patriot Act (2001) created significant new exceptions to search warrant rules. At the end of 2004, the Supreme Court had not ruled on the constitutionality of the act or its several provisions.
— David J. Bodenhamer
