INTRODUCTION The reasonable expectation of privacy test is the central mystery of Fourth Amendment law. According to the Supreme Court, the Fourth Amendment regulates government conduct that violates an individual's reasonable expectation of privacy. (1) But no one seems to know what makes an expectation of privacy constitutionally "reasonable." The Supreme Court has repeatedly refused to offer a single test. (2) The Court has noted that "concepts of real or personal property law" might be relevant, as well as "understandings that are recognized and permitted by society." (3) But the Court has elsewhere rejected property as a guide, (4) and no one knows when society might opt to "recognize" or "permit" something. Who is "society," and how do Supreme Court Justices know what it thinks? Although four decades have passed since Justice Harlan introduced the test in his concurrence in Katz v. United States, (5) the meaning of the phrase "reasonable expectation of privacy" remains remarkably opaque.
