My dad's new car has deadlocks. As far as I can tell, all this means is that the lock pips are flush with the door card when the door's locked, and that they're unlocked using the central locking motors via a signal from a microswitch that's triggered when you pull the door handle.
I assume that when you deadlock the car by pressing the plipper twice, all that happens is the microswitches are ignored, so that the doors can't be unlocked by breaking the window and pulling the handle.
Am I right or wrong? If I'm right, it seems like it'd be pretty easy to retrofit to my car when I fit an alarm.