Why not have a bluetooth/wifi/customised proximity device constantly connected to your laptop (and resides in your wallet/shoes/private parts) and if you suddenly are too far away from your laptop while it's unlocked it gets purged?
* https://www.crowdsupply.com/alt-shift/buskill
When I designed BusKill, I intentionally avoided wireless solutions.
BusKill is designed for situations where the risk is extremely high, and you'll find that the radio-based solutions aren't very secure. They're faulty and have huge surface areas of attack.