Your mobile phone can give away your location, even if you tell it not to

US military officials were recently caught off guard by revelations that servicemembers’ digital fitness trackers were storing the locations of their workouts – including at or near military bases and clandestine sites around the world. But this threat is not limited to Fitbits and similar devices. My group’s recent research has shown how mobile phones can also track their users through stores and cities and around the world – even when users turn off their phones’ location-tracking services.

The vulnerability comes from the wide range of sensors phones are equipped with – not just GPS and communications interfaces, but gyroscopes and accelerometers that can tell whether a phone is being held upright or on its side and can measure other movements too. Apps on the phone can use those sensors to perform tasks users aren’t expecting – like following a user’s movements turn by turn along city streets.