RadiusLocker

RadiusLocker is a free open source app that automatically locks your phone when your smartwatch falls out of connection range, and then temporarily disables biometric unlocking until you've next entered your PIN.

The goal is to further lock down your phone if it gets taken away from you, or if you've left it behind somewhere, thus adding an extra layer of security on local data. Think of it as automation for the Lockdown feature, which temporarily disables biometric unlocking features, but also available for devices running older Android versions behind P.

There is also a Wear OS companion app, which can be used to lock your phone manually while still in range, and both apps can be used just for this if you are not interested in any extra/automated functionality.