Katz v. United States, 389 U.S. 347 (1967), is a landmark decision of the U.S. Supreme Court in which the Court redefined what constitutes a "search" or "seizure" with regard to the Fourth Amendment to the U.S. Constitution. The ruling expanded the Fourth Amendment's protections from an individual's "persons, houses, papers, and effects," as specified in the Constitution's text, to include any areas where a person has a "reasonable expectation of privacy." The reasonable expectation of privacy standard, now known as the Katz test, was formulated in a concurring opinion by Justice John Marshall Harlan II.
The Katz test has since been used in numerous cases, particularly because of technological advances that create new questions about privacy norms and government surveillance of personal data.
Background
Charles Katz was a sports bettor who by the mid-1960s had become "probably the preeminent college basketball handicapper in America". In 1965, Katz regularly used a public telephone booth near his apartment on Sunset Boulevard in Los Angeles to communicate his gambling handicaps to bookmakers in Boston and Miami. Unbeknownst to him, the FBI had begun investigating his gambling activities and was recording his conversations via a covert listening device attached to the outside of the phone booth. After recording many of his phone calls, FBI agents arrested Katz and charged him with eight counts of knowingly transmitting wagering information by telephone between U.S. states, which is a federal crime under Section 18 of the United States Code, particularly a law on the transmission of wagering information.
Katz was tried in the U.S. District Court for the Southern District of California. Katz moved to suppress the FBI's recordings, arguing that because the agents did not have a search warrant allowing them to place their listening device, the recordings had been made in violation of the Fourth Amendment and should be inadmissible in court per the exclusionary rule. The judge denied Katz's motion and held that the recordings were admissible as evidence, and Katz was convicted based on them. Katz then appealed to the Supreme Court, which granted certiorari.
Opinion of the court
On December 18, 1967, the Supreme Court issued a 7–1 decision in favor of Katz that invalidated the FBI's wiretap evidence and overturned Katz's criminal conviction.
The Supreme Court then surveyed the history of American jurisprudence on governmental searches and seizures. It described how American courts had traditionally analyzed Fourth Amendment searches by comparing them to the long-established doctrine of trespass. In their legal briefs, the parties had focused on the 1928 precedent Olmstead v. United States, in which the Court ruled that surveillance by wiretap without any trespass did not constitute a "search" for Fourth Amendment purposes. However, the Court stated that in later cases it had begun recognizing that the Fourth Amendment applied to recorded speech obtained without any physical trespassing, and that the law had evolved. Stewart wrote:
Stewart then concluded the Court's opinion by ruling that even though the FBI knew there was a "strong probability" that Katz was breaking the law when using the phone booth, their use of the wiretap was an unconstitutional search because they did not obtain a warrant before placing the listening device. This overturned Katz's criminal conviction as a constitutional violation.
Harlan's concurrence
thumb|upright=0.9|right|Justice [[John Marshall Harlan (1899–1971)|John Marshall Harlan II, whose concurring opinion created the two-part "Katz test" that is regularly applied in Fourth Amendment cases]]
Justice John Marshall Harlan II's concurring opinion in Katz has become more influential than the majority opinion. The concurrence introduced a two-part test that has come to be known as the Katz test.
Harlan began his opinion by noting that he was writing separately to elaborate on the meaning of Stewart's majority opinion. Harlan explained that he interpreted Stewart's statements that "the Fourth Amendment protects people, not places" and "what a person knowingly exposes to the public [...] is not a subject of Fourth Amendment protection" to mean that the Fourth Amendment is activated any time a person has a reasonable expectation of privacy in the eyes of society at large.
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The Supreme Court adopted Harlan's two-part test as a formulation of the Fourth Amendment search analysis for most subsequent cases involving governmental searches that generated constitutional challenges.
Black's dissent
Justice Hugo Black was the only dissenter in the decision. He argued that the Fourth Amendment was only meant to protect "things" from physical search and seizure, and was not meant to protect personal privacy. Additionally, Black argued that the modern act of wiretapping was analogous to the act of eavesdropping, which was common even when the Bill of Rights was drafted. Black concluded that if the drafters of the Fourth Amendment had meant for it to protect against eavesdropping they would have included the proper language. The Katz precedent continues to be consulted regularly to interpret disputes over modern electronic surveillance by the National Security Agency and law enforcement entities, though with some concerns that the Katz test is becoming outdated due to modern surveillance technologies.
However, Katz also created significantly more uncertainty surrounding the application of the Fourth Amendment. The Katz test of an objective "reasonable expectation of privacy," which has been widely adopted by U.S. courts, has proven much more difficult to apply than the traditional analysis of whether a physical intrusion into "persons, houses, papers, and effects" occurred. In a 2007 Stanford Law Review article, legal scholar Orin Kerr described the scholarly consensus that the Katz test has been a failure:
Other legal scholars have praised Katz as "the king of surveillance cases" due to Stewart's holding that "the Fourth Amendment protects people, not places." They also state that this case stood as a "bulwark against wiretaps and other emerging forms of surveillance."