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.
In Harris v. United States, 1 it 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 with 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 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.