The Supreme Court established the reasonable expectation of privacy test in Katz v. United States (1967), redefining when the Fourth Amendment protects against searches. Justice Harlan created a two-part test: first, a person must show an actual subjective expectation of privacy, and second, society must recognize that expectation as reasonable. This test expanded Fourth Amendment protections beyond the text's specific list of persons, houses, papers, and effects to include any area where someone has a reasonable privacy expectation.
The Court ruled that what someone knowingly exposes to the public, even at home, gets no Fourth Amendment protection. But what someone seeks to preserve as private, even in public areas, may be protected. This shifted Fourth Amendment analysis from property-based trespass to privacy-based expectations, making electronic surveillance subject to constitutional requirements.
The reasonable expectation of privacy test determines what the government needs a warrant to access. As surveillance technology leaps ahead of 1960s-era case law, courts are deciding whether cell tower location data, smart home audio, and license plate readers require warrants — and their answers define the practical scope of the Fourth Amendment today.
People think the Fourth Amendment protects anything they want kept private. What matters legally is whether a court finds society considers that expectation "reasonable." Courts have repeatedly held that information voluntarily shared with third parties — phone companies, banks, internet providers — loses Fourth Amendment protection under the third-party doctrine.
The reasonable expectation of privacy test determines what the government needs a warrant to access. As surveillance technology leaps ahead of 1960s-era case law, courts are deciding whether cell tower location data, smart home audio, and license plate readers require warrants — and their answers define the practical scope of the Fourth Amendment today.
People think the Fourth Amendment protects anything they want kept private. What matters legally is whether a court finds society considers that expectation "reasonable." Courts have repeatedly held that information voluntarily shared with third parties — phone companies, banks, internet providers — loses Fourth Amendment protection under the third-party doctrine.