Wireless keys have made cars much easier to use, but that system can also easily be abused by thieves, which can use range extenders to easily open up a car (and even start it) even if the legitimate key is hundreds of meters away.
The technique is amazingly simple, and similar to what many people use at home to improve their wireless networks using WiFi repeater or range extenders. Wireless car keys are made to work just a few meters away from the car; what this ADAC system allows, is to create a gateway that can extend that range hundreds of meters more.
This means one of the thieves needs only to get close enough to the key, while the other remains close to the car, fooling the car into thinking the real key is close by. For cars with wireless ignition system, this method allows the thieves to start the car and simply drive away (the car will soon complain about the key not being in range, but it will keep moving until you turn it off again - you wouldn't want to be stuck in a highway should your key run out of batteries, would you?)
Car manufactures better start protecting against this kind of technique... though that won't do much to help the thousands (millions?) of vulnerable cars out there in the streets.