The Emerging Principles of Fourth Amendment Privacy

Abstract

The Fourth Amendment applies when the government violates a citizen’s “reasonable expectation of privacy.” But the Supreme Court has never explained what makes an expectation of privacy reasonable, and scholars regularly complain that this standard is incomprehensible and unworkable.

Yet the reasonable expectation of privacy standard may be more coherent than is currently recognized. The Supreme Court has decided more than forty reasonable expectation of privacy cases since the standard was developed. This Article is the first to analyze all of these decisions. It draws out three consistent principles that drive the Court’s assessments of Fourth Amendment privacy: the intimacy of the place or thing targeted; the amount of information sought; and the cost of the investigation.

The Article traces these principles through the Court’s Fourth Amendment jurisprudence, offering an explanatory account of a body of law often thought to be inexplicable. And it brings them forward, generating predictions for future cases involving novel surveillance technologies.

The Article makes several contributions to the Fourth Amendment literature. It develops a unified model of Fourth Amendment privacy, one that operates consistently across a variety of surveillance contexts. It details the Supreme Court’s growing acknowledgment of the principles of intimacy, amount, and cost. It makes the case for more overt recognition of these principles, which would have substantial benefits for Fourth Amendment jurisprudence and scholarship. And it offers a clear, comprehensible answer to the question of what violates a reasonable expectation of privacy.

Keywords: Fourth Amendment, Privacy, Katz, Drones, Facial Recognition, Smart Homes, Carpenter, Searches, Surveillance, Intimacy, Reasonable, Supreme Court

JEL Classification: K14