Your cellphone tracks your location everywhere you go. Whether law enforcement officials should have access to that data is at the center of a constitutional debate, says NPR. Matt Blaze, a professor of computer and information science at the University of Pennsylvania, says that, “As you move around, your phone is constantly checking to see whether the tower that it’s currently registered with is the best one, or whether there’s a better tower with a stronger signal coming in range.” Cellphone companies store that information so they can deliver better service. Law enforcement subpoenas phone location data regularly. Subpoenas are “part of almost every major case, including homicide, in some cases, sexual assault, drug trafficking cases,” says Jake Wark of the Suffolk County, Ma., District Attorney’s office. The National Security Agency says it does not track the location of cellphones but that it would be legal to collect that information. Shabazz Augustine is accused of murdering an ex-girlfriend nine years ago. Massachusetts prosecutors want to use information they got about the location of his cellphone. Matt Segal of the American Civil Liberties Union says the evidence should be thrown out because police got it using a simple subpoena, not a search warrant.