There was an interesting documentary on ITV last night regarding how car crime is increasing. Although much of the increase is due to targeted burglaries where the keys are stolen, they also attributed the fact that many cars now have keyless entry and the availability of gadgets which can boost the signal from the key. The criminals are theoretically able to open and start the car while the key is still in te house.
One of the security features manufacturers have developed is a motion sensor in the key which controls the radio signal. They showed a Mercedes where the key was placed on the bonnet of the car. The doors would not unlock until the key was picked up. I have just tested this with my A3 key and got the same result. Who knew?