What is Umwelt?
Umwelt allows to lock or unlock your PC automatically with a Android phone or smartwatch, by sensing Bluetooth proximity.
If using a phone, you can disable proximity and use the fingerprint reader, allowing to unlock the PC with the phone in your pocket.
It also sends a warning if anyone tries to steal your laptop and the phone/watch is within Bluetooth range.
The Mac version can use any BtLE device but has less functionality.