Download btprox from the sourceforge website and start the installer.
You can keep the original destination folder and click on Install and close it when it is finished.
Now pair your phone with your laptop by bluetooth. You can do this by rightclicking on the bluetooth icon and clicking on add a bluetooth device. Now select your phone (You have to enable bluetooth and make your phone visible first)
After this we start the btproxy.exe from the C:\Program Files (x86)\BtProx folder
Select your phone at Used device
Now you can add the lock command in the Lock command box. The command to lock your system is: rundll32.exe user32.dll,LockWorkStation
Now press Start and your all set.
When you reboot the system BTprox will autostart.