Unauthorized tracking devices, including those that change their identification information periodically, are detected to protect an individual's privacy. A mobile device of a user detects a first advertisement signal from an unknown wireless device, the first advertisement signal containing information representative of the unknown device. Multiple advertisement signals may be received as the mobile device moves a distance greater than a broadcast range away from the location where the first signal was detected. Responsive to detecting a second advertisement signal containing the same identity information after the mobile device has moved at least the distance greater than the broadcast range away from the location where the first signal was detected, the system generates an interface on the mobile device. The generated interface indicates to a user of the mobile device the presence of an unknown device.