Google Bluetooth Distance Measurement API and Watch Unlock Feature
Google is reportedly working on a new Android feature called the Bluetooth distance measurement API, which uses Bluetooth’s Received Signal Strength Indicator (RSSI) to measure the distance between a phone and a connected device. The feature code is already added to the Android Open Source Project (AOSP) as a Project Mainline module.
The Bluetooth distance measurement API will allow users to know how far their Bluetooth accessories are from their smartphones, making it a useful tool for features like Watch Unlock. However, it should be noted that this API will not be a highly precise way to measure distance, but it should be good enough for Watch Unlock and other functionality.

The Watch Unlock feature, as described by Mishaal Rahman, will allow users to unlock their phone using their watch if the watch is unlocked, on their wrist, and nearby (about 1 meter, based on Bluetooth RSSI). This feature would activate after face/fingerprint recognition fails to unlock the phone.
While the Bluetooth distance measurement feature has been added to the AOSP, it is a non-updatable module in Android 13, which means that it may not be available to devices through a future extension SDK. This also means that the Watch Unlock feature may not use this new framework API, assuming it launches while Pixels are still on Android 13.
Google has confirmed that it is working on the Watch Unlock feature but has not announced when it will be released to the public. Overall, the Bluetooth distance measurement API and Watch Unlock feature represent exciting new developments in the world of Android, offering users more convenience and security when it comes to their device and accessory interactions.