Kaz, we have an alarm too which we had installed when we first moved in and used it at religiously at first but then we got Bill and assumed the PIRs would detect him if it was set when he was mooching around the house when home alone (shutting him in a room with no PIRS doesn't work because he can use door handles regardless of whether the door's got to be pushed or pulled open).
Jen and Matt up the corner were broken into before we moved here. They sold up and the people who bought their house (who everyone thinks are dodgy) have also been broken into and on that occasion the thieves took the woman's bag containing the keys to her top of the range new BMW which obviously then got driven away. The problem with that house is it's sort of hidden away off the end of the cul de sac and two thirds of the back garden and the whole of the front are accessible over the fence from the common.