Hi mate & anyone else that's interested. I had a word with my mate regarding the baby monitor that he uses in his garage and he says it's a BT100 digital baby monitor. He says it has saved his bikes a few times. If you Google "BT100 baby monitor" you should get a few results of places selling them, Amazon currently have them on offer at £42.27. If you don't keep your car in a garage you could always leave the monitor in the car as it says it is very sensitive and the sound is excellent.
Hope this helps someone to hold on to their car.