The Supreme Court has ruled that police need a search warrant to obtain data showing the location of cell phone users. Similar to rulings made in 2012 and 2014, the Supreme Court rejected the argument that police should have the same access as investigators do in order to examine business records held in banks or conduct physical surveillance. The ruling stated the “world of difference” between 1970s decisions allowing the limited personal information obtained in accessing business records and today’s digital records.

The Wall Street Journal quotes Chief Justice John Roberts, who wrote in the 5-4 opinion that, “when the government tracks the location of a cell phone it achieves near perfect surveillance, as if it had attached an ankle monitor to the phone’s user.”

“Unlike the nosy neighbor who keeps an eye on comings and goings,” he added, “the signal towers and processing centers that track cell phone users ‘are ever alert, and their memory is nearly infallible’, making analog-era precedents prosecutors cited to justify such warrantless searches all but obsolete.”

In its 2012 decision, the court ruled that, “police had conducted a search when they surreptitiously attached a GPS tracker to a suspect’s vehicle, triggering Fourth Amendment protections against illegal searches.”

In 2014, the court ruled that, “authorities generally need a warrant to search the contents of a cell phone found in a suspect’s pocket, despite precedents allowing police to examine address books, matchboxes and other items found on an arrestee without demonstrating probable cause.”

In the most recent ruling, conservative justices Anthony Kennedy, Clarence Thomas, Samuel Alito and Neil Gorsuch filed four separate dissents; only liberal judges supported Roberts.

WSJ notes that the ruling “applied one of the court’s best-known yet most enigmatic constitutional doctrines — that Fourth Amendment protections against police searches hinge on the public’s ‘reasonable expectation of privacy’, as Justice John Marshall Harlan put it in a 1967 opinion.” Roberts previously advocated for caution towards “big data” and “robots.” Still, Roberts has also noted that the ruling “does not call into doubt” the warrantless searches related to “bomb threats, active shootings, and child abductions.”

The Electronic Frontier Foundation reported that AT&T and Verizon “combined receive more than 100,000 law-enforcement requests a year for cell-location information, and a majority of those requests come without a warrant.” More than a dozen technology companies — including Apple, Dropbox, Facebook, Google, Microsoft and Verizon — filed a brief arguing that “the court should adopt strong Fourth Amendment protections for digital data.”