From the article:

> The current approach taken by smartphone companies to make the devices hard to track by their Bluetooth signals is to randomly change the phone’s identity, its MAC address. However, that doesn’t address the physical-layer fingerprints inherent in each device’s transmissions.. All wireless devices have small manufacturing imperfections in the hardware used to emit these beacons.. These imperfections in Bluetooth hardware result in unique distortions, which can be used as a fingerprint to track a specific device.