460 U.S. 276 (1983)
United States v. Knotts is a foundational Fourth Amendment decision defining the limits of privacy in one's movements on public roads and the permissible use of then-novel tracking technology.
Does the warrantless monitoring of a beeper to track a suspect's movements on public roads constitute a "search" or "seizure" under the Fourth Amendment requiring a warrant?
A person traveling on public thoroughfares has no reasonable expectation of privacy in his movements from one place to another. The warrantless use of electronic tracking (a beeper) to monitor a vehicle's location on public roads is not a Fourth Amendment search where the monitoring reveals only information that could have been obtained through visual surveillance. The Court reserved the question whether monitoring a beeper within a private residence or other constitutionally protected space would constitute a search.
No. Monitoring the beeper to track the container's and vehicle's movements on public highways did not constitute a Fourth Amendment search, so no warrant was required. The Supreme Court reversed the judgment of the court of appeals.
Knotts firmly establishes the public-exposure principle for location tracking: short-term electronic monitoring of a vehicle's movements on public roads is not a search. This rule undergirds much of modern Fourth Amendment doctrine concerning technology and surveillance. Yet Knotts also contains a limiting signal: it leaves open whether surveillance that invades the home or that amounts to pervasive, long-term monitoring raises distinct privacy concerns. Those caveats became pivotal in United States v. Karo (1984) (monitoring beeper signals inside a home is a search), United States v. Jones (2012) (physical trespass to install a GPS device is a search), and Carpenter v. United States (2018) (long-term historical CSLI acquisition is a search). For law students, Knotts is a cornerstone case for understanding Katz, the difference between public and private spaces, and how courts treat sense-enhancing technologies that track location.