US Constitution

Charles Katz was convicted in California of illegal gambling. He had used a public pay phone booth in Los Angeles to place bets in Miami and Boston. Unbeknownst to Katz, the FBI had recorded his conversation via an electronic eavesdropping device attached to the exterior of the phone booth. Katz was convicted based on recordings of his end of the conversations. He challenged his conviction, arguing that the recordings could not be used as evidence against him. The Court of Appeals sided with the FBI because there was not a physical intrusion into the phone booth itself. The Supreme Court granted certiorari.

The majority in Katz changed how the Fourth Amendment was interpreted. Prior to Katz a physical intrusion into some protected space was required before the Fourth Amendment was violated. In Katz, the police had bugged an enclosed phone booth in such a way that there was no physical intrusion, but they could overhear what Mr. Katz was saying inside the booth. The majority ruled that the Fourth Amendment protects people, not places. They ruled that Mr. Katz had a "reasonable expectation of privacy" inside the enclosed phone booth; and that the Fourth Amendment had been violated since the police did not have a search warrant.

The citation is Katz v. United States, 389 US 347 (1967).