We had a spate of burglaries in peoples houses whilst the people were sleeping in the house in our area. We've got 3 kids and the bedrooms are separated over the first and top floor so we installed a wireless yale alarm mainly to alert us whilst we're in the house asleep and secondly as a deterrent. None of our neighbours have alarms and we made the assumption the opportunistic burglar would choose a house without an alarm over a house with. The alarm we got is good, it's very loud indoors and out and calls us if the alarm goes off. We've had a number of false alarms due to the placement of one of the IR sensors in the sun lounge, if theres a sudden temperature shift (hot sunny day, sun goes behind cloud, temperature drops, sun comes out of cloud, temperature rises and the sensor thinks someones in the sun lounge).
Alarm is the Yale wireless set, we got it for about £150 on one of the homebase special discount weekends.