iOS 13 ‘Find My’ combines Find My Friends and Find My iPhone. Apple says it uses Bluetooth signals from Apple devices even if they’re offline. And the encryption scheme it uses means that third party attackers can’t track Apple devices, and Apple can’t track them either.
In a background phone call with WIRED following that keynote, Apple broke down that privacy element, explaining how its “encrypted and anonymous” system avoids leaking your location data willy nilly, even as your devices broadcast a Bluetooth signal explicitly designed to let you track your device. The solution to that paradox, it turns out, is a trick that requires you to own at least two Apple devices. Each one emits a constantly changing key that nearby Apple devices use to encrypt and upload your geolocation data, such that only the other Apple device you own possesses the key to decrypt those locations.