#47 · 2026-09-22 · Case
Katz v. United States
Answer: Katz v. United States, 389 U.S. 347 (1967). The Court held that warrantless electronic eavesdropping on a public phone booth is a Fourth Amendment search because the Amendment protects people, not places. ([law.cornell.edu](https://www.law.cornell.edu/supremecourt/text/389/347)) Justice Harlan’s concurrence articulated the two-part reasonable-expectation-of-privacy test. ([law.cornell.edu](https://www.law.cornell.edu/constitution-conan/amendment-4/katz-and-reasonable-expectation-of-privacy-test?utm_source=openai)) The decision reaffirmed the warrant preference, allowing only narrow exceptions. ([law.cornell.edu](https://www.law.cornell.edu/supremecourt/text/389/347)) States may set higher search-and-seizure protections under their own constitutions but cannot undercut the federal floor. ([law.cornell.edu](https://www.law.cornell.edu/wex/fourth_amendment?utm_source=openai))
Rule to remember
Katz v. United States (1967) held that the Fourth Amendment “protects people, not places” and that warrantless electronic eavesdropping on a public phone booth is a search; Harlan’s concurrence introduced the two-part reasonable-expectation-of-privacy test.
Key elements and checks
- Fourth Amendment protection turns on privacy, not property or location.
- No physical trespass is required; electronic monitoring can be a search.
- Two-part test: subjective expectation of privacy + objective reasonableness.
- Warrant preference: searches outside the judicial process are presumptively unreasonable, with limited exceptions.
- What is knowingly exposed to the public is unprotected; efforts to preserve privacy in public may be protected.
- States may provide greater protections under state constitutions, though federal Katz standards set the constitutional floor.
In the source’s words
“the Fourth Amendment protects people, not places.”
Katz v. United States, 389 U.S. 347 (1967) | LII
“What a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection.”
Katz v. United States, 389 U.S. 347 (1967) | LII
State variation: Many states interpret their own search-and-seizure clauses to afford more protection than the federal baseline, but none may authorize conduct violating the federal Fourth Amendment.