The developer by the name of Wuul has developed an awesome application called Blue Lock that I am sure would be used by everyone. It is fairly simple app that locks the computer when no bluetooth device is found.
Here is how it works, you run the portable app and it will start detecting all bluetooth devices near your computer. Select the mobile device from the list and it will add the hardware information in the “Lock Device” field.
Now it will search for this locked device every few seconds(depending on what timeout you have selected), when it is not detected the computer will be immediately locked down.
In practical terms it is very useful, sometimes we are in rush and don’t have time to hit Win + L key to lock the computer. Now you can just grab your cellphone and rush away, when the bluetooth is out of range it will automatically lock the computer after the timeout is complete. Note that I tested it with my iPhone and it worked perfectly fine.
The only downside is that some bluetooth devices are quite powerful and your computer might not lock even when you are on the other end of the office or when you are simply roaming around the house.
It works on all versions of Windows. Enjoy!