In which case was the reasonable expectation of privacy standard established?

The reasonable expectation of privacy standard was established in Katz v. United States. This landmark Supreme Court case defined the concept of privacy in relation to the Fourth Amendment, which protects individuals from unreasonable searches and seizures.

In Katz, the Court ruled that the government's recording of a conversation from a public phone booth constituted a search under the Fourth Amendment. The pivotal part of the decision was the introduction of the reasonable expectation of privacy standard, where the Court determined that the Fourth Amendment protects people, not just places. This meant that if an individual has a reasonable expectation of privacy in a particular situation, any governmental intrusion into that situation could be considered a search that requires a warrant or probable cause.

Katz broadened the scope of Fourth Amendment protections beyond physical trespass to include a person's privacy interests, establishing a critical framework for evaluating cases involving the search and seizure of information or items through technology and other means. Thus, any subsequent case involving Fourth Amendment issues often references the principles established in Katz regarding privacy expectations.