Katz v. United States (1967): The Reasonable Expectation of Privacy

Case at a Glance

Katz v. United States: The Complete Case Brief

Katz v. United States is the 1967 Supreme Court case that redefined the Fourth Amendment to protect people, not just places. The Supreme Court ruled 7-1 that the FBI's warrantless use of an electronic listening device on a public phone booth violated Charles Katz's constitutional rights, even though the government never physically entered the booth. This case is commonly searched as katz v united states, katz v us, or katz vs us case, and it remains one of the most cited Fourth Amendment decisions in American law.

What Laws Was Mr. Katz Accused of Breaking?

Charles Katz was accused of transmitting wagering information by telephone across state lines, in violation of 18 U.S.C. § 1084, a federal law against interstate gambling communications. Katz, suspected of being a bookmaker, regularly used a public phone booth in Los Angeles to place illegal bets. Without obtaining a warrant, FBI agents attached an electronic listening and recording device to the outside of the phone booth Katz used and recorded his end of several conversations. That recorded evidence was introduced at his trial and used to convict him.

Procedural History

Katz was convicted at trial, and his lawyers argued the recordings should have been suppressed because they were obtained without a warrant. The trial court allowed the evidence, and Katz was convicted. He appealed to the U.S. Court of Appeals for the Ninth Circuit, which affirmed his conviction, reasoning that because the FBI agents never physically entered the phone booth, there was no unconstitutional search under existing Fourth Amendment doctrine at the time.

Katz then petitioned the Supreme Court, which granted certiorari. Oral argument was held on October 17, 1967, and the Supreme Court issued its decision on December 18, 1967.

The Legal Issue

The central issue was whether the Fourth Amendment's protection against unreasonable searches and seizures applies to electronic surveillance of a conversation, even when there is no physical trespass into a private space. The government argued that because the phone booth was a public space made of glass, Katz had no reasonable expectation of privacy there, and that the Fourth Amendment traditionally protected only tangible, physical areas such as homes and offices. Katz argued that the phone booth functioned as a private space for the duration of his call, regardless of its public location.

The Holding

Yes. The Supreme Court held that the Fourth Amendment's protection from unreasonable search and seizure extends to any area where a person has a reasonable expectation of privacy, and that physical intrusion is not required for a search to occur. The Court reversed Katz's conviction because the government's failure to obtain a warrant before attaching the listening device made the search unconstitutional.

The Court's Reasoning

Justice Potter Stewart wrote the majority opinion, joined by Chief Justice Warren and Justices Douglas, Harlan, Brennan, White, and Fortas. Justice Thurgood Marshall did not participate in the case.

The Fourth Amendment Protects People, Not Places

The Court's most famous line from the opinion is that the Fourth Amendment "protects people, not places." Stewart explained that what a person seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected, while what a person knowingly exposes to the public is not protected, even inside a private home.

Physical Intrusion Is Not Required

The Court rejected the idea that a Fourth Amendment search requires the government to physically penetrate a protected space. This directly overruled the reasoning from earlier decisions like Olmstead v. United States and Goldman v. United States, which had focused on whether officers committed a physical trespass. Attaching a listening device to the outside of the phone booth, without any physical intrusion inside it, still counted as a search because it captured a conversation Katz reasonably intended to keep private.

Katz Had a Reasonable Expectation of Privacy in the Booth

The Court found that Katz's expectation of privacy in the phone booth was reasonable, even though the booth was located in a public place. By entering the booth and shutting the door, Katz sought to exclude the "uninvited ear," and the Court held that society was prepared to recognize that expectation as legitimate.

Warrantless Searches Are Presumptively Unreasonable

The Court held that warrantless searches are "per se unreasonable" under the Fourth Amendment, subject only to a few narrow, well-established exceptions. Because the FBI could have sought a warrant from a neutral magistrate before conducting the surveillance but chose not to, the search was unconstitutional regardless of whether probable cause may have existed.

Justice Harlan's Concurrence and the Reasonable Expectation of Privacy Test

Justice John Marshall Harlan II's concurring opinion introduced what became known as the "reasonable expectation of privacy" test, which has become the standard framework courts use to apply Katz today. Harlan explained the test has two parts:

1. A person must have exhibited an actual, subjective expectation of privacy.
2. That expectation must be one that society is prepared to recognize as reasonable.

Harlan illustrated the test by noting that a person's home is a place where privacy is expected for most purposes, while objects or activities knowingly exposed to public view are not protected, since no intention to keep them private was ever shown. Conversations held out in the open, where anyone could overhear them, would not be protected, because expecting privacy under those circumstances would not be reasonable.

The Dissent

Justice Hugo Black dissented, arguing that the Fourth Amendment's text was written to protect tangible things, "persons, houses, papers, and effects," and was never intended to cover intangible conversations captured through eavesdropping technology. Black believed it was not the Supreme Court's role to rewrite the Fourth Amendment to keep pace with new technology, arguing that such changes should come through legislation rather than judicial reinterpretation.

Why Katz v. United States Matters

Katz v. United States is significant because it shifted Fourth Amendment analysis away from physical trespass and toward a person's reasonable expectation of privacy, a change that continues to shape how courts evaluate government surveillance today.

Key reasons the case remains important:

• It created the "reasonable expectation of privacy" test, still the primary framework for Fourth Amendment search analysis.
• It extended constitutional protection to electronic surveillance and wiretaps, not just physical searches of property.
• It overruled the property-based trespass doctrine established in earlier wiretapping cases.
• It requires law enforcement to obtain a warrant before most forms of electronic monitoring, absent a recognized exception.
• It continues to influence modern surveillance cases, including disputes over cell phone location tracking, thermal imaging, and digital privacy, such as Kyllo v. United States (2001).

Katz v. United States and Modern Privacy Law

The reasonable expectation of privacy test from Katz remains the foundation for nearly every modern Fourth Amendment surveillance case. Courts continue to apply Harlan's two-part framework when evaluating new surveillance technologies, from GPS tracking devices to cell-site location data. Because Katz established that the Fourth Amendment follows the person rather than the property, it has allowed constitutional protections to adapt as technology has evolved far beyond the rotary phone booths of the 1960s.

Key Facts at a Glance

Frequently Asked Questions

What was Katz v. United States about?

Katz v. United States was about whether the FBI's warrantless use of a listening device on the outside of a public phone booth to record Charles Katz's conversations violated the Fourth Amendment.

What was the ruling in Katz v. United States?

The Supreme Court ruled 7-1 that the Fourth Amendment protects people, not just places, and that warrantless electronic surveillance of Katz's phone booth conversations violated his constitutional rights.

What laws was Mr. Katz accused of breaking?

Katz was accused of transmitting wagering information by telephone across state lines in violation of federal gambling law, 18 U.S.C. § 1084.

What year was Katz v. United States decided?

The Supreme Court decided Katz v. United States on December 18, 1967.

Who wrote the majority opinion in Katz v. United States?

Justice Potter Stewart wrote the majority opinion.

What is the reasonable expectation of privacy test?

It is a two-part test from Justice Harlan's concurrence requiring that a person show an actual, subjective expectation of privacy, and that this expectation be one society recognizes as reasonable.

What does "the Fourth Amendment protects people, not places" mean?

It means Fourth Amendment protection depends on whether a person reasonably expected privacy in a given situation, rather than on whether the government physically entered a specific type of location.

Did the FBI physically enter the phone booth in Katz v. United States?

No. The FBI attached the listening device to the outside of the booth without any physical intrusion inside it, which the Court still ruled constituted a search.

Who dissented in Katz v. United States?

Justice Hugo Black dissented, arguing the Fourth Amendment's text was meant to protect only tangible items and spaces, not overheard conversations.

What case did Katz v. United States overrule?

Katz v. United States effectively overruled the physical trespass doctrine established in Olmstead v. United States and Goldman v. United States.

Why is Katz v. United States important today?

It remains important because its reasonable expectation of privacy test is still the primary standard courts use to evaluate modern government surveillance, including digital and electronic monitoring.

What court heard Katz's case before the Supreme Court?

The U.S. Court of Appeals for the Ninth Circuit affirmed Katz's conviction before the Supreme Court agreed to hear the case.

What is the short summary of Katz v. United States?

In short, the Supreme Court ruled that recording someone's conversation with a hidden device, even in a public phone booth and without physical trespass, is a search under the Fourth Amendment and generally requires a warrant.

Did Justice Thurgood Marshall participate in Katz v. United States?

No, Justice Thurgood Marshall took no part in the consideration or decision of the case.

What is the citation for Katz v. United States?

The case is cited as Katz v. United States, 389 U.S. 347 (1967).

Final Takeaway

Katz v. United States transformed Fourth Amendment law by moving the focus away from physical property and trespass and toward a person's reasonable expectation of privacy. By ruling that the FBI's warrantless recording of Charles Katz's phone booth conversations was an unconstitutional search, the Supreme Court established a flexible standard, refined by Justice Harlan's concurring test, that continues to guide how courts evaluate government surveillance in an age of rapidly evolving technology.