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You got a warrant? For cops tracking cellphones, the answer should be yes

Courts have set a low standard for obtaining cellphones’ “metadata”— information on who you’re calling, what time you’re calling, or the physical locations of those on the line.

Chris Ratcliffe/Bloomberg/File 2016

Courts have set a low standard for obtaining cellphones’ “metadata”— information on who you’re calling, what time you’re calling, or the physical locations of those on the line.

Imagine owning a rewind button that lets you review every significant event of your life. Now imagine that rewind button in the hands of the FBI or the IRS or the Boston police.

If the idea makes you uncomfortable, you’ve got company, including the US Supreme Court.

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On Monday, the high court agreed to hear a case that’ll examine whether federal investigators should have gotten a warrant before using cellphone location data to hit rewind on the movements of two criminal suspects. The data proved the two men had been in the wrong places at the right times. But everybody with a cellphone generates the same kind of digital map, revealing every move we’ve made. If police can review this data whenever they choose, any of us could be subjected to retroactive surveillance, with little judicial oversight.

Between 2010 and 2011, Timothy Carpenter and Timothy Sanders rampaged through multiple Radio Shack and T-Mobile stores in Michigan and Ohio, stealing — of all things — cellphones. But their own phones betrayed them. Cellphones track our location relative to nearby cell towers. When MetroPCS and, yes, T-Mobile gave the FBI several months’ worth of Carpenter’s and Sanders’ phone records, it included location data that helped prove their guilt. Sanders got 14 years, while Carpenter drew a 116-year sentence because he’d used a gun in the commission of multiple federal felonies.

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But the FBI didn’t request a warrant, which requires convincing a judge that the target of the search is probably involved in a crime. You need a warrant to listen to calls. But courts have set a lower standard for obtaining “metadata”— information on who you’re calling, what time you’re calling, or the physical locations of those on the line.

Metadata became a household word in 2013, when former National Security Agency contractor Edward Snowden revealed that the secret US agency was indiscriminately scooping up the phone call data of millions of Americans. The resulting outrage led to legislation halting the metadata collections.

But domestic police agencies keep on using metadata on a smaller scale. To get it, they merely tell a judge that the data is relevant to an investigation.

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In this case, the FBI scooped up 88 days of Sanders’ phone records and 127 days of Carpenter’s, then mapped the location of those phones minute-by-minute. It was like putting a tail on the two men, but without the shoe leather.

But did the FBI go too far? The Supreme Court ruling that granted easy access to metadata was issued in the pre-cellular world of 1979, when police could only get the addresses of fixed landline phones. Today’s phones go where we go, constantly tracking our whereabouts whenever they are switched on, not just when we make calls.

Four decades ago, this only happened in spy movies. Today, it happens to everybody. Should police be able to view such sensitive data with the bare minimum of judicial oversight?

A federal appeals court said yes and upheld the convictions, but not without some resistance. One judge worried that the FBI might have gone too far and hinted that the Supreme Court should take up the matter. And so it shall.

Massachusetts resolved this question back in 2014, when the state’s Supreme Judicial Court held that police must have a warrant to collect cellphone location data. And though the matter remains unsettled at the federal level, the Supremes have been tuning up for a case like this for years.

In 2012, the high court ruled unanimously that police couldn’t plant a GPS location tracker on a suspect’s car without a warrant. But conservative Justice Samuel Alito and his liberal colleagues Ruth Bader Ginsburg, Stephen Breyer, and Elena Kagan wanted to go much further. In a concurring opinion, Alito noted that the police could have gotten the same information by capturing GPS data from the suspect’s own phone. He argued that today’s phones make possible the kind of constant surveillance that should not be conducted without a warrant.

A ruling against the FBI could lead to limits on other kinds of rewind surveillance. Consider those license plate cameras used by police forces throughout the United States. They’re good for tracking stolen cars and scofflaws. But if cities deploy them in many locations, and retain each photo for years, the police could conduct after-the-fact snooping on millions of motorists. By punching in a license plate number, an investigator could instantly know if you drove north on I-93 back in April 2015. There’s no federal regulation of these cameras; only 15 states have passed laws of their own, according to the National Conference of State Legislatures. Massachusetts is not among them, though a bill is pending on Beacon Hill.

I’m hoping Carpenter and Sanders win and perhaps inspire a compromise that defends privacy without hamstringing police. Maybe courts would make it easy for investigators to do a week’s worth of electronic backtracking. But for deeper searches, they’d demand a warrant. I don’t mind the cops hitting the rewind button now and then; just don’t go wearing it out.

Hiawatha Bray can be reached at hiawatha.bray@globe.com. Follow him on Twitter @GlobeTechLab.
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