Almost 10 years ago I wrote a Windows Vista Sidebar Gadget which I called Bluetooth Auto Lock Gadget. It was based off a Coding4Fun project called Bluetooth Screen Lock. Over its life in the Windows Gadget store it had over 50,000 downloads at my last check up until Microsoft discontinued gadgets in Windows 7 due to security concerns and their then new direction into Live Tiles.
On the Windows Insider updates they just announced:
Introducing Dynamic Lock: Dynamic Lock automatically locks your Windows 10 PC when you’re not around based the proximity of a Bluetooth-paired phone. If your Bluetooth-paired phone is not found near your PC, Windows turns off the screen and locks the PC after 30 seconds. To enable Dynamic Lock, make sure your phone is paired to your PC via Bluetooth and go to Settings > Accounts > Sign-in options and toggle Dynamic lock to “on”.
It was a useful gadget and I’m pleased to see this functionality will now be available built-in to Windows 10.