Katz v. United States
The Court ruled that recording a person's conversation in a public telephone booth, without a warrant, violated the Fourth Amendment, because the Amendment protects people's reasonable expectations of privacy wherever they are, not just their physical property.
The decision replaced an older rule that had let the government eavesdrop electronically as long as agents didn't physically break into a protected space, and it discarded the idea that only certain 'constitutionally protected areas' get Fourth Amendment coverage.
“For the Fourth Amendment protects people, not places.”
The Court's core reframing of what the Fourth Amendment actually protects.
How it got here: A federal trial court convicted the man; the Ninth Circuit affirmed, finding no Fourth Amendment violation because agents never physically entered the booth; the Supreme Court agreed to hear the case.
The Case in Depth
What happened
A man was convicted of illegally transmitting gambling information by phone across state lines. FBI agents, without a warrant, attached a listening and recording device to the outside of a public telephone booth he regularly used and recorded his end of several calls. He argued that using his own recorded words against him at trial violated his constitutional rights, since agents never physically entered the booth.
The question before the Court
Could FBI agents record a man's phone calls by attaching a listening device to a public phone booth, without ever getting a warrant?
The Court's answer
No — the government violated the Fourth Amendment by recording the man's phone conversations without a warrant, even though agents never physically entered the phone booth. The Court held that the Fourth Amendment protects people's reasonable expectations of privacy, not just physical spaces or tangible property, so a person who shuts a phone booth door and pays to make a call is entitled to assume his words won't be intercepted.
Because agents had time to seek approval from a judge beforehand but didn't, the surveillance was unreasonable regardless of how careful and limited it was. This overturned the older rule that let the government eavesdrop electronically as long as there was no physical trespass, replacing it with a broader privacy-based test that still governs surveillance law today.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Anyone using a phone booth, or any enclosed space, gained protection against secret government recording without a warrant. Law enforcement agencies nationwide had to start seeking judicial approval before wiretapping or bugging conversations, reshaping how criminal investigations involving electronic surveillance are conducted to this day.
What changes now
The conviction was reversed because the wiretap evidence should not have been admitted without a warrant. The ruling is a final merits decision, not temporary, and it establishes a lasting framework — the reasonable-expectation-of-privacy test — that lower courts have used ever since to decide when government surveillance requires prior judicial approval. The Court explicitly left open how this framework applies to national-security surveillance.
What this does not decide
The Court expressly said it was not deciding whether warrantless electronic surveillance could be justified in cases involving national security, leaving that question for another day. It also did not address the law of arrest, detention, or the validity of a separate search warrant for the petitioner's premises.
Concurrences and dissents
Concurrence — Justice Douglas
Justice Douglas joined the majority but wrote to reject Justice White's suggestion that the President or Attorney General could authorize warrantless national-security wiretaps. He argued the Executive Branch is an interested party, not a neutral magistrate, and that the Fourth Amendment draws no distinction between types of crimes, so no special national-security exception should exist.
Concurrence — Justice Harlan
Justice Harlan agreed with the result but articulated the enduring two-part test for Fourth Amendment protection: a person must show an actual, subjective expectation of privacy, and that expectation must be one society recognizes as reasonable. He also urged that Olmstead and Goldman be explicitly overruled rather than left ambiguously eroded.
Concurrence — Justice White
Justice White agreed the surveillance here was unreasonable without a warrant, but emphasized that the decision does not reach national-security wiretapping, suggesting warrantless surveillance authorized by the President or Attorney General for national-security reasons could still be reasonable without judicial approval.
Dissent — Justice Black
“A conversation overheard by eavesdropping, whether by plain snooping or wiretapping, is not tangible and, under the normally accepted meanings of the words, can neither be searched nor seized.”Black's textual objection to extending the Fourth Amendment to cover eavesdropped conversations.
Justice Black argued the Fourth Amendment's text protects only tangible things capable of being searched and seized, so eavesdropping on conversations falls outside its scope entirely. He accused the majority of rewriting the Amendment to fit modern policy preferences about privacy rather than interpreting its actual words, and argued Olmstead and Goldman had never truly been eroded by later cases.
How the Court got there
The legal reasoning, step by step
- The Court rejected framing the issue around whether a telephone booth was a 'constitutionally protected area,' explaining that the Fourth Amendment protects people, not places, so the right question is whether a person had a reasonable expectation of privacy in what happened, regardless of the physical space involved.
- The Court reasoned that a person who enters a phone booth, shuts the door, and pays to make a call is entitled to assume his words won't be broadcast to the world, even though the booth is glass-walled and he remains visible to passersby.
- Because earlier decisions had allowed warrantless electronic eavesdropping only when there was no physical trespass into a protected space, the Court concluded that the trespass requirement no longer controlled: the government's electronic listening and recording, even without physically penetrating the booth, still counted as a 'search and seizure.'
- Applying the Fourth Amendment's general rule that searches without prior judicial authorization are presumptively unreasonable, the Court found that even though the agents acted with restraint and had probable cause, they never sought approval from a neutral magistrate before listening, and no established exception (like hot pursuit, arrest, or consent) applied to excuse that omission.
- The Court concluded that because the surveillance was conducted without the antecedent judicial authorization the Fourth Amendment requires, it was unconstitutional, regardless of how narrowly the agents limited their own conduct.
Doctrinal impact
Cases affected by this decision
Overrules Olmstead v. United States (277 U.S. 438)
The ruling that warrantless wiretapping without physical trespass was constitutional is no longer good law.
Overrules Goldman v. United States (316 U.S. 129)
The ruling that non-trespassory electronic eavesdropping fell outside Fourth Amendment protection is discarded.
Reaffirms Silverman v. United States (365 U.S. 505)
The Court relies on this case's recognition that eavesdropping can be a search even without seizing physical property.
Reaffirms Berger v. New York (388 U.S. 41)
The Court builds on this case's requirements for lawful judicially authorized electronic surveillance.