Your Phone's Battery Use Lets Spies Track Your Movements Spies and cops can use your smartphone to track your movements. That's no mystery—most smartphones come with a GPS chip that makes it pretty damned simple. So if you don't want to be tracked, you just turn off the GPS feature, right? Unfortunately, there is another way prying eyes can follow your movements: through your Android phone's battery. A team of security researchers from Stanford and the Israeli government just published the details of a technique that lets spies watch you as you move around by monitoring tiny changes in your phone's battery levels. It all comes down to how hard your phone has to work to ping cell towers. The towers that are further away or obscured by a building or hill cause your phone to use a little bit more power. So if—and this is a big "if"—the spies know your normal routine, they can track your movements with 90 percent accuracy. If they don't know your routine, that accuracy drops to about 60 percent.