The case in one breath In 1965, a Los Angeles gambler named Charles Katz stepped into a public phone booth, pulled the door shut, and placed his bets. What he didn’t know: FBI agents had attached a listening device to the outside of the booth and were recording his end of the calls. They never went inside. They never asked a judge. Under the old rule, that meant no searchSearch: in Fourth Amendment law, a government intrusion on something you’re entitled to keep private. If it counts as a search, the government usually needs a warrant first. had happened at all. In 1967, the Supreme Court threw that rule out. The Fourth Amendment, it said, protects people, not places. What matters is not whether the government physically trespassed — it’s whether it invaded privacy you were entitled to count on. Katz is where the phrase reasonable expectation of privacyReasonable expectation of privacy: the test from Justice Harlan’s concurrence — you actually expected privacy, and society is prepared to call that expectation reasonable. comes from, and courts still reach for it every time a new gadget makes spying easier.
Decided
December 18, 1967
Vote
7–1
Opinion by
Justice Stewart
Protects
People, not places
The Story Behind Katz v. United States
It started with a man, a pay phone, and a door he thought was enough.FEB 1965FBI agents in Los Angeles are watching Charles Katz, a professional sports gambler. They notice a habit: at about the same time each morning, he walks to a public phone booth on Sunset Boulevard, steps in, and makes a few short calls.
THE BUGThe agents attach an electronic listening and recording device to the outside of the booth and switch it on only during Katz’s morning window. The haul: six recordings, about three minutes each, of his end of calls about placing bets. Nobody asks a judge for a warrantWarrant: a judge’s written permission for a search, issued in advance. The FBI had none here — and that is what sank the case..
THE TRIALKatz is charged under an eight-count federal indictment with transmitting wagering information by telephone from Los Angeles to Miami and Boston. He objects to the recordings. The judge lets them in, and he’s convicted.
THE APPEALThe Ninth Circuit Court of Appeals sides with the government for one reason: the agents made no physical entrance into the space Katz occupied. That was the law since Olmstead v. United States in 1928 — no trespass, no search. Katz takes it to the Supreme Court.
OCT 17, 1967The case is argued at the Supreme Court. Both sides treat it as a fight over whether a phone booth is a “constitutionally protected area.” The government stresses the glass: Katz was as visible inside the booth as outside it.
DEC 18, 1967The Court rules 7–1 for Katz and reverses his conviction. Justice Marshall takes no part. The trespass rule is finished as the only test.
The Question the Court Faced in Katz v. United States
For almost forty years, the Fourth Amendment question was basically a property question: did the government physically intrude on something of yours — your house, your papers, your things? No intrusion, no search. But technology had made breaking in unnecessary. A device on the outside of a wall could hear everything said on the inside. So the question: when the government secretly listens to a private conversation without ever setting foot in your space, has it “searched” anything? And if it has, does it need a judge’s permission first?
What the Court Decided in Katz v. United States
Yes, and yes — starting with eight words that rewired the Fourth Amendment:“For the Fourth Amendment protects people, not places.”— Justice Stewart, for the Court
Stewart said both sides were asking the wrong question. Whether a phone booth counts as a protected place isn’t the point — what the person tried to keep private is. “What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection.” What he tries to keep private, even somewhere the public can go, may be. So the glass didn’t matter. Katz wasn’t hiding from eyes — he was shutting out, in Stewart’s phrase, “the uninvited ear.” Someone who steps into a booth, “shuts the door behind him, and pays the toll that permits him to place a call” is entitled to assume his words “will not be broadcast to the world.” Then the old rule fell: the trespass doctrine from Olmstead “can no longer be regarded as controlling.” The device never pierced the booth’s wall, and that made no difference — recording Katz’s words was a search and seizure. The agents had been careful, listening only during his window, and the Court said a judge could have approved this exact surveillance. But that restraint was “imposed by the agents themselves, not by a judicial officer.” No warrant, no conviction. The twist: the famous Katz test isn’t in the majority opinion. It comes from Justice Harlan’s short concurrence:
“My understanding of the rule that has emerged from prior decisions is that there is a twofold requirement, first that a person have exhibited an actual (subjective) expectation of privacy and, second, that the expectation be one that society is prepared to recognize as ‘reasonable.'”— Justice Harlan, concurring
1. You actually expected privacy — you acted like it, the way Katz did when he shut the door, and 2. Society is prepared to call that expectation reasonable — it isn’t just your personal wish. Harlan’s own example of the limit: a conversation held out in the open isn’t protected. Later courts adopted his two-part version as the working test. Justices White and Douglas (joined by Brennan) added concurrences sparring over national security surveillance, which the majority said this case didn’t present. Justice Black dissented alone. To him, the Amendment covers tangible things that can be searched and seized, and a conversation is neither. He did not think it was “the proper role of this Court to rewrite the Amendment” to keep up with the times. That argument never fully went away.
What Katz v. United States Means for You
✓ BECAUSE OF KATZ
- The Fourth Amendment covers your private conversations — not just your house and your physical stuff
- The government doesn’t have to break in or touch anything to “search” you — secretly listening in counts
- Privacy can travel with you — the Court named a business office, a friend’s apartment, a taxicab, and a phone booth
- Officers being careful isn’t enough — the judge’s approval has to come before the listening, not after
- Courts ask the Katz question about new technology, including the location records in Carpenter
✗ KATZ DOESN’T MEAN
- Everything you’d like kept private is protected — the expectation has to be one society accepts as reasonable
- What you knowingly expose to the public is covered — a conversation held out in the open is fair game
- Police can never listen — with a warrant they can, and the Court said a judge could have approved this very recording
- The Fourth Amendment is a general “right to privacy” — the Court said flatly that it can’t be turned into one
- It protects you from other people — the opinion left snooping by private individuals largely to state law
Questions People Ask About Katz v. United States
What is the “reasonable expectation of privacy” test?
It’s a two-part question from Justice Harlan’s concurrence. First: did you actually expect privacy, and act like it? Second: is that an expectation society is prepared to recognize as reasonable? If both answers are yes and the government intrudes anyway, that’s a search — and searches usually need a warrant.
Why did it matter that Katz closed the door?
Because it showed what he was trying to keep private. The booth was partly glass, so anyone could watch him. The Court answered that he wasn’t blocking eyes — he was blocking ears. Harlan called a phone booth “a temporarily private place” while you’re in it. Shut the door, pay for the call, and you’ve done what a person does to keep a conversation private.
What was Olmstead, and did Katz overrule it?
Olmstead v. United States (1928) was a Prohibition-era bootlegging case. Federal agents tapped phone lines in an office building basement and on the streets near the defendants’ homes, without trespassing on their property. Chief Justice Taft, writing for a 5–4 Court, said the Fourth Amendment didn’t apply: “There was no searching. There was no seizure.” Katz ended that reasoning.
Could the FBI have recorded Katz legally?
Yes — and that’s the part people miss. The Court never said police can’t listen in. It said a judge, told what the agents knew and planned, could have authorized this same limited surveillance. The agents skipped that step. Katz isn’t a ban on surveillance. It’s a rule about who approves it: a neutral judge, in advance — not the officers doing the listening.
Does Katz protect my phone, my texts, and my location?
Not directly — Katz is about a 1960s pay phone. But later cases grow from the same root. In Riley v. California (2014), the Court held police generally need a warrant to search the contents of a phone taken during an arrest. In Carpenter (2018), it used the Katz test to protect months of phone location records. Our phone tracking guide picks up from there.
What happened to Charles Katz?
He won. The Supreme Court reversed his conviction because the recordings behind it were made without a warrant. The opinion ends there, so we won’t guess at the rest. What’s certain is where his name ended up: on the test judges still use to decide what the government can learn about you without asking a judge first.
Key Terms in Katz v. United States, Explained
Search — a government intrusion on something the Fourth Amendment protects; after Katz, that includes private conversations.
Reasonable expectation of privacy — Harlan’s two-part test: you actually expected privacy, and society accepts that expectation as reasonable.
Trespass doctrine — the older rule that a search required a physical intrusion on your property; Katz said it no longer controls.
Warrant — a judge’s advance permission for a search. The FBI’s failure to get one is why Katz won.
Concurrence — a separate opinion by a justice who agrees with the result but adds their own reasoning. The Katz test comes from one.
Cases Connected to Katz v. United States
United States v. Jones (2012)The property rule comes back. Agents tracked a Jeep by GPS for 28 days; the Court called it a search because the government physically occupied private property to get information — and said Katz was added to the trespass test, not swapped in for it.Read the full case → Riley v. California (2014)From the phone booth to the phone in your pocket: a unanimous Court held police generally need a warrant to search a phone taken during an arrest.Read the full case → Carpenter v. United States (2018)The Katz test meets the smartphone: people have a reasonable expectation of privacy in the record of their movements, so police generally need a warrant for historical cell-site location records.Read the full case →Olmstead v. United States (1928)The rule Katz ended: a 5–4 Court held that tapping phone lines without trespassing on the defendants’ property was no search at all.
Chatrie v. United States (2026)The newest chapter: the Court applied the Katz test again and held that getting a man’s Google location data through a geofence warrant was a search.
What’s Still Undecided After Katz v. United States
Katz is nearly sixty years old and still the working test — but its foundations are being argued over. As of October 2026:
- Privacy test, property test, or both? — Jones revived the property approach in 2012 and said Katz sits on top of it. That leaves two routes to calling something a search, and no single rule for how they fit together.
- Whether the test should survive — some current justices say no. Dissenting in Carpenter, Justice Thomas wrote: “The Katz test has no basis in the text or history of the Fourth Amendment.” In Chatrie, in June 2026, Justice Gorsuch agreed only with the result: he argued the Katz test should be set aside and would ask instead whether the data was the person’s own papers or effects. The Chatrie majority kept applying Katz. For now, it remains the law.
- How it applies to new technology — a test built around a phone booth door has been stretched over a heat-sensing camera aimed at a house (Kyllo, 2001), cell-site records, and Google location data. The Court moves one technology at a time and leaves the next question open: in Chatrie it found a search, then sent the case back to decide whether the warrant was valid.
Why this page exists: Almost every argument about your digital privacy — your phone, your location, your data — runs back to a man in a phone booth in 1965. Most explanations of Katz assume you went to law school. This one assumes you own a phone. The facts and quotations above come from the Court’s own opinions, linked below so you can check us.
The Bottom Line on Katz v. United States
A gambler shut a phone booth door, the FBI listened from outside the glass, and the Supreme Court changed the question the Constitution asks: not “did the government trespass?” but “did it invade privacy you were entitled to count on?” That question has limits — what you put out in public stays public, and a warrant still opens the door. It has critics, too — the property rule is back beside it, and some justices want it gone. But for now, when a court decides whether the government can listen, track, or collect, it starts where Charles Katz did. Now you know.Your practical guideCan police track your phone? → The modern sequelCarpenter v. United States → More casesBrowse all court case files →
Sources
Primary sources:- Katz v. United States, 389 U.S. 347 (1967) — full opinion — supreme.justia.com
- Katz v. United States — case summary — oyez.org
- Olmstead v. United States, 277 U.S. 438 (1928) — supreme.justia.com
- United States v. Jones, 565 U.S. 400 (2012) — supreme.justia.com
- Carpenter v. United States, 585 U.S. 296 (2018) — supreme.justia.com
- Kyllo v. United States, 533 U.S. 27 (2001) — case summary — oyez.org
- Chatrie v. United States, No. 25-112 (2026) — supreme.justia.com
- Katz v. United States — background on the investigation — National Constitution Center
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