Katz v. United States

Charles Katz was convicted of transmitting wagering information by telephone across state lines. At trial, the government used recordings of Katz's side of calls that FBI agents captured by attaching an electronic listening and recording device to the outside of a public phone booth he used.

The lower court upheld the conviction because agents had not physically entered the booth.

The dispute reached the courts because the police action, prosecution, civil-rights claim, or government policy raised a constitutional question that could not be answered by the facts alone.

Does the Fourth Amendment apply to government electronic listening and recording of a person's conversations from a public phone booth when officers do not physically trespass into the booth?

In plain English, the court had to decide where police authority ended and constitutional protection began under the facts of this case.

Yes. The Court held that the government's electronic surveillance violated the privacy Katz justifiably relied on while using the phone booth and was a Fourth Amendment search and seizure. Physical trespass is not required. Warrantless electronic surveillance is unconstitutional unless a recognized exception applies.

The decision matters because katz shifted Fourth Amendment law away from a property-only trespass model and toward protection of reasonable expectations of privacy. It established that law enforcement generally needs prior judicial authorization for electronic surveillance, even when officers use careful methods and do not physically enter a protected space.

The Fourth Amendment protects people, not just places. If a person reasonably expects privacy in a conversation, police usually need a warrant before secretly recording it.

Katz remains central to disputes over wiretaps, phones, location data, digital monitoring, and surveillance technology. Its reasonable-expectation-of-privacy framework still shapes how courts evaluate searches in both physical and digital settings.