KeyLock is a free Windows tool which allows you to lock your PC with a USB flash drive. If you need to leave it unattended for a while, just unplug the drive, a custom lock screen appears, and you won’t be able to continue until it’s reconnected.
Setup is easy. Connect a USB key, choose it in the Drives list, and you can save the details and start protection in a couple of clicks.
The core engine works as described. Unplug the drive and your desktop is almost immediately replaced by a warning dialog. You can’t Alt+Tab or use Task Manager to bypass it.
Built-in event logging lists any attempts to access the system, and you can even enable audio recordings, perhaps helping you figure out who the attacker might be.
There’s an option to start KeyLock with Windows. This is turned off by default, but enable it and the program is launched when your system starts, so rebooting alone won’t give a snooper access.
We wouldn’t rely on KeyLock too much, as a determined attacker will soon find a way in. Booting in Safe Mode is one route, switching to another user account may be another, and there are other potential weak points, too.
Still, if you just want an extra layer of protection to stop family or co-workers accessing your computer when you’re away for a moment -- and the regular Win+L Windows lock screen isn’t enough -- KeyLock should work very well.