What significant precedent was established in Katz v. United States?

The case of Katz v. United States significantly established the principle that a warrant is necessary for electronic surveillance, which fundamentally impacted the Fourth Amendment's interpretation regarding privacy and searches. In Katz, the Supreme Court held that individuals have a reasonable expectation of privacy in their conversations, even when those conversations occur in a public phone booth. This ruling emphasized that the government's interception of communications violated this privacy expectation, thus requiring a warrant grounded in probable cause before such surveillance can be deemed lawful.

This decision marked a pivotal shift in understanding the application of constitutional protection against unreasonable searches and seizures, extending to technologies not originally imagined by the framers of the Constitution. Consequently, after Katz, law enforcement agencies must demonstrate probable cause and obtain warrants to conduct electronic surveillance of private communications, aligning modern practices with the protections intended by the Fourth Amendment.