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The Supreme Court will decide when the police can use your phone to track you

Chatrie v. United States asks what limits the Constitution places on the surveillance state in an age of cellphones.

Check your pocket. You’re probably carrying a tracking device that will allow the police — or even the Trump administration — to track every move that you make.

If you use a cellphone, you are unavoidably revealing your location all the time. Cellphones typically receive service by connecting to a nearby communications tower or other “cell site,” so your cellular provider (and, potentially, the police) can get a decent sense of where you are located by tracking which cell site your phone is currently connected with. Many smartphone users also use apps that rely on GPS to precisely determine their location. That’s why Uber knows where to pick you up when you summon a car.

Get the latest developments on the US Supreme Court from senior correspondent Ian Millhiser.

Nearly a decade ago, in Carpenter v. United States (2018), the Supreme Court determined that law enforcement typically must secure a warrant before they can obtain data revealing where you’ve been from your cellular provider. On Monday, April 27, the Court will hear a follow-up case, known as Chatrie v. United States, which raises several questions that were not answered by Carpenter.

For starters, when police do obtain a warrant allowing them to use cellphone data, what should the warrant say — and just how much location information should the warrant permit the police to learn about how many people? When may the government obtain location data about innocent people who are not suspected of a crime? Does it matter if a cellphone user voluntarily opts into a service, such as the service Google uses to track their location when they ask for directions on Google Maps, that can reveal an extraordinary amount of information about where they’ve been? Should internet-based companies turn over only anonymized data, and when should the identity of a particular cellphone user be revealed?

More broadly, modern technology enables the government to invade everyone’s privacy in ways that would have been unimaginable when the Constitution was framed. The Supreme Court is well aware of this problem, and it has spent the past several decades trying to make sure that its interpretation of the Fourth Amendment, which constrains when the government may search our “persons, houses, papers, and effects” for evidence of a crime, keeps up with technological progress.

As the Court indicated in Kyllo v. United States (2001), the goal is to ensure the “preservation of that degree of privacy against government that existed when the Fourth Amendment was adopted.” More advanced surveillance technology demands more robust constitutional safeguards.

But the Court’s commitment to this civil libertarian project is also precarious. Carpenter, the case that initially established that police must obtain a warrant before using your cell phone data to figure out where you’ve been, was a 5-4 decision. And two members of the majority in Carpenter, Justices Ruth Bader Ginsburg and Stephen Breyer, are no longer on the Court (although Breyer was replaced by Justice Ketanji Brown Jackson, who generally shares his approach to constitutional privacy cases). Justice Neil Gorsuch also wrote a chaotic dissent in Carpenter, suggesting that most of the past six decades’ worth of Supreme Court cases interpreting........

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