Primary Source: Katz v. United States (1967)

Katz v. United States addresses whether the Fourth Amendment’s prohibition on unreasonable searches and seizures applies to electronic eavesdropping and wiretapping of a public phone booth. Acting on a suspicion that Charles Katz was transmitting gambling information over the phone to clients in other states, federal agents attached an eavesdropping device to the outside of a public phone booth used by Katz. Based on recordings of his end of the conversation, Katz was convicted for illegal gambling. Katz argued that the government violated the Fourth Amendment by listening in on his conversation. As public phone booths and electronic communications became more common in American life, the Supreme Court had to determine whether and how to apply a constitutional text written in 1791 to the technological changes of modern life. Today, such questions persist as to when the government can obtain cell phone data from cell phone providers, and whether they can search a smartphone containing all the intimate details of one’s life.

[T]he Fourth Amendment protects people, not places. What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection. But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.

The Government stresses the fact that the telephone booth from which the petitioner made his calls was constructed partly of glass, so that he was as visible after he entered it as he would have been if he had remained outside. But what he sought to exclude when he entered the booth was not the intruding eye—it was the uninvited ear. He did not shed his right to do so simply because he made his calls from a place where he might be seen. No less than an individual in a business office, in a friend’s apartment, or in a taxicab, a person in a telephone booth may rely upon the protection of the Fourth Amendment. One who occupies it, shuts the door behind him, and pays the toll that permits him to place a call is surely entitled to assume that the words he utters into the mouthpiece will not be broadcast to the world. To read the Constitution more narrowly is to ignore the vital role that the public telephone has come to play in private communication. . . .

[O]nce it is recognized that the Fourth Amendment protects people—and not simply ‘areas’—against unreasonable searches and seizures it becomes clear that the reach of that Amendment cannot turn upon the presence or absence of a physical intrusion into any given enclosure. . . .

The Government’s activities in electronically listening to and recording the petitioner’s words violated the privacy upon which he justifiably relied while using the telephone booth and thus constituted a ‘search and seizure’ within the meaning of the Fourth Amendment. The fact that the electronic device employed to achieve that end did not happen to penetrate the wall of the booth can have no constitutional significance. . . .

As the Court’s opinion states, ‘the Fourth Amendment protects people, not places.’ The question, however, is what protection it affords to those people. Generally, as here, the answer to that question requires reference to a ‘place.’ My understanding of the rule that has emerged from prior decisions is that there is a twofold requirement, first 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.’ Thus a man’s home is, for most purposes, a place where he expects privacy, but objects, activities, or statements that he exposes to the ‘plain view’ of outsiders are not ‘protected’ because no intention to keep them to himself has been exhibited. On the other hand, conversations in the open would not be protected against being overheard, for the expectation of privacy under the circumstances would be unreasonable.

The critical fact in this case is that ‘(o)ne who occupies it, (a telephone booth) shuts the door behind him, and pays the toll that permits him to place a call is surely entitled to assume’ that his conversation is not being intercepted. The point is not that the booth is ‘accessible to the public’ at other times, but that it is a temporarily private place whose momentary occupants’ expectations of freedom from intrusion are recognized as reasonable. . .

The first clause [of the Fourth Amendment] protects ‘persons, houses, papers, and effects, against unreasonable searches and seizures . . . ’ These words connote the idea of tangible things with size, form, and weight, things capable of being searched, seized, or both. The second clause of the Amendment still further establishes its Framers’ purpose to limit its protection to tangible things by providing that no warrants shall issue but those ‘particularly describing the place to be searched, and the persons or things to be seized.’ A conversation overheard by eavesdropping, whether by plain snooping or wiretapping, is not tangible and, under the normally accepted meanings of the words, can neither be searched nor seized.

[B]y arbitrarily substituting the Court’s language, designed to protect privacy, for the Constitution’s language, designed to protect against unreasonable searches and seizures, the Court has made the Fourth Amendment its vehicle for holding all laws violative of the Constitution which offend the Court’s broadest concept of privacy. . . . No general right is created by the Amendment so as to give this Court the unlimited power to hold unconstitutional everything which affects privacy. Certainly the Framers, well acquainted as they were with the excesses of governmental power, did not intend to grant this Court such omnipotent lawmaking authority as that. The history of governments proves that it is dangerous to freedom to repose such powers in courts.