Vice President JD Vance holds a highly sophisticated tracking device that the government can use to monitor his every move. | Jonathan Ernst-Pool/Getty Images 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.

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 the Fourth Amendment are wrong. So it’s fair to say that Gorsuch is a wild card whose vote in Chatrie is difficult to predict. It remains to be seen, in other words, whether the Supreme Court is still committed to preserving Americans’ privacy even as technology advances — and whether there are still five votes for the civil libertarian approach taken in Carpenter.

Geofence warrants, explained Chatrie concerns “geofence” warrants, court orders that permit police to obtain locational data from many people who were in a certain area at a certain time. During their investigation of a bank robbery in Midlothian, Virginia, police obtained a warrant calling for Google to turn over location data on anyone who was present near the bank within an hour of the robbery. The warrant drew a circle with a 150-meter radius that included both the bank and a nearby church.

Google had this information because of an optional feature called “Location History,” which tracks and stores where many cellphones are located. This data can then be used to pinpoint users who use apps like Google Maps to help them navigate, and also to collect data that Google can use to determine which ads are shown to which customers. The government emphasizes in its brief that “only about one-third of active Google account holders actually opted into the Location History service,” while lawyers for the defendant, Okello Chatrie, point out that “over 500 million Google users have Location History enabled.” The warrant also laid out a three-step process imposing some limits on the government’s ability to use the location information it obtained. At the first stage, Google