In Olmstead v. United States[c]Olmstead v. United States a 5-4 decision in 1928, the Supreme Court held that conversations were not protected by the Fourth Amendment because they are not tangible objects that can be seized. The Court further ruled that if the tapping of a telephone conversation occurs without the police entering into a private home, there is no “search” of a constitutionally protected area. In dissent, Justice Louis D. BrandeisBrandeis, Louis D.;on privacy[privacy] wanted to interpret the Fourth and Fifth Amendments to protect the privacy of individuals, not just material objects. However, the Court reaffirmed the Olmstead ruling in Silverman v. United States[c]Silverman v. United States (1961), declaring that in order for a Fourth Amendment search to take place, the police must physically intrude into “a constitutionally protected area.”

Around that same time, federal agents attached an electronic listening device to the outside of a public phone booth frequently used by bookmaker Charles Katz. The conversations overheard by the officers were used in his criminal trial. Katz argued that the listening devices violated his Fourth Amendment protection against illegal searches. The lower courts, referring to Olmstead and Silverman, concluded that no search had occurred, because no tangible object was involved and the wall of the booth had not been physically penetrated.

By a 7-1 margin, however, the Supreme Court ruled in Katz’s favor. Delivering the opinion for the Court, Justice Potter StewartStewart, Potter;Katz v. United States argued that the agents had intruded into Katz’s privacy, thereby conducting a search and seizure according to the Fourth Amendment, which required a warrant from a neutral magistrate. He further explained that “the Fourth Amendment protects people, not places,” and that the information a person “seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected.” In an often quoted concurring opinion, Justice John Marshall HarlanHarlan, John Marshall;Katz v. United States wrote more broadly of a “reasonable expectation of privacy.” He stated that this expectation was based on two things: that the person’s actions indicate an expectation of privacy, and that the expectation is one judged by society to be reasonable.

The seminal Katz ruling, as interpreted in Harlan’s concurrence, provided the standard for deciding countless later Fourth Amendment cases. The Court, however, has tended to take a relatively narrow interpretation of the concept “reasonable expectation of privacy.” For example, it found that a person had no reasonable expectation of privacy in bank records in United States v. Miller[c]Miller, United States v. (1976), because the information is voluntarily given to banks and is exposed to the banks’ employees. In California v. Ciraolo[c]California v. Ciraolo (1986), the Court found that people have no reasonable expectation of privacy against warrantlessWarrantless searches police surveillance by a helicopter flying over a fenced backyard. Likewise, in Minnesota v. Carter (1998), the Court held that temporary visitors in a home, unlike the homeowner, did not have any reasonable expectation of privacy.

Fourth Amendment

Kyllo v. United States

Mapp v. Ohio

Privacy, right to

Search warrant requirement

Stewart, Potter