Reasonable Expectation of Privacy

Reasonable expectation of privacy is a core concept in Fourth Amendment law that often determines whether a person has a privacy interest in a certain location, whether there has been a Fourth Amendment violation, or whether there has even been a search in the first place. Justice John Marshall Harlan II coined the phrase in his concurring opinion in the wiretapping case Katz v. United States (1967).

Harlan wrote that suspected bookie Charlie Katz had a reasonable expectation of privacy in an “enclosed telephone booth.” He then articulated a two-part test for determining whether someone has a reasonable expectation of privacy: (1) whether the defendant has an actual subjective expectation of privacy and (2) whether society recognizes that expectation as objectively reasonable.

Legal commentator Peter Winn explains: “Within a decade, Harlan's test became so familiar that the Court officially recognized it as the essence of the Katz decision—a rare instance where a concurrence effectively replaced a majority opinion” (2009, 7). The U.S. Supreme Court used the term “reasonable expectation of privacy” in numerous Fourth Amendment decisions and contexts in the 1970s, including South Dakota v. Opperman (1976) involving the inventory search of a vehicle; Marshall v. Barlow's, Inc. (1978), involving the unlawful warrantless search of a business; and Michigan v. Tyler (1978), involving searches by fire officials.

The Court has used Justice Harlan's test in other Fourth Amendment contexts. For example, the Court determined in California v. Ciraolo (1986) that a defendant had no reasonable expectation of privacy when the police flew over his home and backyard at an altitude of 1,000 feet. By contrast, in Bond v. United States (2000), the Court determined that a law-enforcement agent's physical manipulation of a person's bag on a bus violated the person's reasonable expectation of privacy.

The doctrine remains a staple of the Court's Fourth Amendment jurisprudence.