From the article: > Mobile devices, including phones, smartwatches and fitness trackers, constantly transmit signals, known as Bluetooth beacons, at the rate o

From the article: > Mobile devices, including phones, smartwatches and fitness trackers, constantly transmit signals, known as Bluetooth beacons, at the rate of roughly 500 beacons per minute. These beacons enable features like Apple’s “Find My”--a tracking service to find a lost device as well as COVID-19 tracing apps; and connect smartphones to other devices such as wireless earphones. > 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 due to unique hardware imperfections. > All wireless devices have small manufacturing imperfections in the hardware used to emit these beacons that are unique to each device. These fingerprints are an accidental byproduct of the manufacturing process. These imperfections in Bluetooth hardware result in unique distortions, which can be used as a fingerprint to track a specific device.