My very nearly stock CAT S60 Android smartphone supports the phone being automatically unlocked if a Bluetooth device you’ve designated as “trusted” is connected, so no, I don’t think it is proprietary. However, it won’t work here. It unlocks, yeah, but doesn’t lock it back if the device goes out of range.
Besides, the cops can take away your trinket as well.
Presumably you could defeat this with a separate partition, as already suggested by many, and I suspect some additional security might help. Perhaps something as simple as triggering a lock if the accelerometer data gets a bit too frisky. After all, they can’t snatch the phone out of your hand gently, that would defeat the point.
