The Supreme Court has delivered a big win for privacy in U.S. v. Jones. That’s the case in which government agents placed a GPS device on a car and used it to track a person round‐​the‐​clock for four weeks. The question before the Court was whether the government may do this in the absence of a valid warrant. All nine justices say No.


That’s big, important news. The Supreme Court will not allow developments in technology to outstrip constitutional protections the way it did in Olmstead.


Olmstead v. United States was a 1928 decision in which the Court held that there was no Fourth Amendment search or seizure involved in wiretapping because law enforcement made “no entry of the houses or offices of the defendants.” It took 39 years for the Court to revisit that restrictive, property‐​based ruling and find that Fourth Amendment interests exist outside of buildings. “[T]he Fourth Amendment protects people, not places” went the famous line from Katz v. United States (1967), which has been the lodestar ever since.


For its good outcome, though, Katz has not served the Fourth Amendment and privacy very well. The Cato Institute’s brief argued to the Court that the doctrine arising from Katz “is weak as a rule for deciding cases.” As developed since 1967, “the ‘reasonable expectation of privacy’ test reverses the inquiry required by the Fourth Amendment and biases Fourth Amendment doctrine against privacy.”


Without rejecting Katz and reasonable expectations, the Jones majority returned to property rights as a basis for Fourth Amendment protection. “The Government physically occupied private property for the purpose of obtaining information” when it attached a GPS device to a private vehicle and used it to gather information. This was a search that the government could not conduct without a valid warrant.


The property rationale for deciding the case had the support of five justices, led by Justice Scalia. The other four justices would have used “reasonable expectations” to decide the same way, so they concurred in the judgement but not the decision. They found many flaws in the use of property and “18th‐​century tort law” to decide the case.


Justice Sotomayor was explicit in supporting both rationales for protecting privacy. With Justice Scalia, she argued, “When the Government physically invades personal property to gather information, a search occurs.” This language—more clear, and using the legal term of art “personal property,” which Justica Scalia did not—would seem to encompass objects like cell phones, the crucial tool we use today to collect, maintain, and transport our digital effects. Justice Sotomayor emphasized in her separate concurrence that the majority did not reject Katz and “reasonable expectations” in using property as the grounds for this decision.


Justice Sotomayor also deserves special notice for mentioning the pernicious third‐​party doctrine. “[I]t may be necessary to reconsider the premise that an individual has no reasonable expectation of privacy in information voluntarily disclosed to third parties.” The third‐​party doctrine cuts against our Fourth Amendment interests in information we share with ISPs, email service providers, financial services providers, and so on. Reconsidering it is very necessary.


Justice Alito’s concurrence is no ringing endorsement of the “reasonable expectation of privacy” test. But he and the justices joining him see many problems with applying Justice Scalia’s property rationale as they interpreted it.


Along with the Scalia‐​authored Kyllo decision of 2001, Jones is a break from precedent. It may seem like a return to the past, but it is also a return to a foundation on which privacy can be more secure.


More commentary here in the coming days and weeks will explore the case’s meaning more fully. Hopefully, more Supreme Court cases in coming years and decades will clarify and improve Fourth Amendment doctrine.