That question arises from today’s opinion in United States v. Jones. In Jones, a divided Supreme Court found that law enforcement violated the Fourth Amendment when it placed a GPS device on a suspect’s car. While the result was not particularly surprising, how the court got there was.
Ever since Katz v. United States, 389 U. S. 347 (1967), the court has answered Fourth Amendment questions by considering whether the government’s action invaded an expectation of privacy protected under the Constitution. Prior to Katz, a Fourth Amendment violation arose only when the government trespassed on an individual’s person, property or papers. In Jones, Justice Scalia reaches back 45 years and resurrects this trespass theory of Fourth Amendment jurisprudence, holding that an unconstitutional search occurred because the officers trespassed by attaching the GPS device to the suspect’s car.
The majority opinion makes clear that it is not doing away with the “privacy” branch of Fourth Amendment jurisprudence, a point Justice Sotomayor drives home in her concurrence. While agreeing that the Fourth Amendment protects against governmental trespass, she makes clear that the Fourth Amendment also protects against governmental intrusion on reasonable expectations of privacy, regardless of whether the government trespasses in the process.
So for now there are two balls in the air — trespass and privacy — and law enforcement must keep their eyes on both!
Tom Goldstein makes an important clarification in this post on the Scotus blog. In Jones the court only decided that a search took place. It did not address if that search required a warrant, finding that the government had failed to preserve that argument below. There are a number of exceptions to the warrant requirement and it is entirely possible that a future opinion of the court could find no warrant required for the short term use of GPS Monitoring. Read Tom’s excellent post for more analysis.