Katz v. United States

The Court held that a “search” takes place whenever the government intrudes on a reasonable expectation of privacy. The Court concluded that the defendant’s expectation of privacy was reasonable if he had taken measures to secure his privacy and the defendant’s expectation of privacy met community standards.

What a person seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected under the Fourth Amendment. A person in a telephone booth may rely upon the protection of the Fourth Amendment, and is entitled to assume that the words he utters into the mouthpiece will not be broadcast to the world.

Once the defendant established he met both prongs, any government intrusion into these areas must meet Fourth Amendment standards. The Fourth Amendment demands that all searches be reasonable. Searches conducted without a warrant are presumed to be unreasonable, except for some limited well-delineated exceptions. In this case, the agents did not have a warrant or valid exception.