Instant locking when bluetooth out of range smart lock

[AC Question]

I've been experimenting with smart lock for my bluetooth smartwatch. The part which concerns me is if my phone is lost or stolen and the screen is unlocked while bluetooth is still in range. As long as the screen remains on the person can continue using the phone, even as it goes out of range of the bluetooth connection.

I don't suppose there is some option so that if the phone goes out of range of a trusted device it will lock, even if the phone is unlocked at the time.