"In 'United States v. Jones,' 132 S. Ct. [Supreme Court] 945 (2012), all nine Supreme Court Justices agreed that Jones was 'searched' when the police attached a Global Positioning System (GPS) device to the undercarriage of his car and tracked his movements for four weeks. The Court, however, splintered on what constituted the search: the attachment of the device or the long-term monitoring. The majority held that the 'attachment' of the GPS device and an attempt to obtain information was the violation; Justice Alito, concurring, argued that the 'monitoring' was a violation of Jones's reasonable expectation of privacy; and Justice Sotomayor, also concurring, agreed with them both, but would provide further Fourth Amendment protections. This report will examine these three decisions in an effort to find their place in the body of existing Fourth Amendment law pertaining to privacy, property, and technology. […] Although all three opinions concluded that the government's action in 'Jones' was a search, none expressly required that police get a warrant in future GPS tracking cases. (The government forfeited the argument.) Further, there is no clear indication of the level of suspicion--probable cause, reasonable suspicion, or something less--that is required to attach a GPS unit and monitor the target's movements."
CRS Report for Congress, R42511