Blue Lock is a small application that works with Bluetooth, and acts like a key that blocks your PC if it doesn´t detect a Bluetooth device close by. You can use it with multiple devices that use this technology, like a mobile phone, for example: once the PC loses connection with the mobile, it blocks itself until you insert the access password.
The program scans and generates a list of devices that are close by, so you can choose and select the one you want to use. It then associates an identifying ID to that device so that Blue Lock will recognize it when it is close to your PC.
The PC blocking is totally secure, the same as doing Ctrl+Alt+Del. Configure your access password and so avoid others getting into your PC while you aren´t there.