Kde comes with a framework that provide a set of software to be used with bluetooh, it is called kbluetooth. It is actually comes with kubuntu by default.
One interesting tools in it is, kbluelock. Basically it is a program that lock the screen, when bluetooth signal from a designated phone disappeared.
You can call it, by right click on the kbluetooth, which is on the system tray,
Right click on it, you should see a few program, Select KBlueLock,
It really don't do much at first, just select the right option will prompt KBlueLock to search for your phone. I just select both. And the phone.
What really cool is, my friend didn't really saw this type of program on windows before, which to me really cool. Someway to show off, linux
One thing is, it is dead easy to configure, another is, well, it take sometime to lock and unlock the screen. And can be a bit limiting