A team from the University of California-San Diego demonstrated for the first time that it's possible to distinguish an individual signal from mobile devices, including smartphones, smartwatches, and fitness trackers. All of these devices constantly transmit signals called "Bluetooth beacons." The devices emit these signals at a rate of 500 beacons per minute and enable features such as Apple's "Find My" lost device tracking device and COVID-19 tracing apps. They also help to connect smartphones and other devices to accessories like wireless headphones.

With previous studies finding that wireless fingerprinting works for WiFi, the team wanted to see if the same could be done with Bluetooth.

"This is important because in today's world Bluetooth poses a more significant threat as it is a frequent and constant wireless signal emitted from all our personal mobile devices," says Nishant Bhaskar, a Ph.D. student in the UC San Diego Department of Computer Science and Engineering, in a university release.

Every Bluetooth signal is unique — but that's not intentional

Study authors explain that every wireless device you own has small manufacturing imperfections in their hardware. These flaws are an accidental byproduct of the manufacturing process and are also unique to every single device. The result creates unique distortions in their signal which act like a fingerprint for every device in the world.

For a hacker, this would allow them to bypass anti-tracking software that constantly changes the address mobile devices use to connect to the Internet. This isn't exactly an easy process. Fingerprinting techniques for WiFi signals have relied on a long-known sequence called the preamble.