The idea of a house alarm is to attract attention. Any thief/burglar is reluctant to break into a house that screams, not because they expect people to intervene or call the cops, but because they expect people to turn around and look, and thus see them, which makes them unwelcome eye witnesses later when the house owners have returned and called the police. Most burglaries are, by their nature, opportunistic crimes because you don't know what you'll get for your efforts until you are actually inside the house. Rich pickings are only guaranteed in difficult, risky (guarded, alarmed and secured) targets, which requires skill and preparation, so burglary is usually about easy targets with small returns. Statistics also show that most burglaries are committed within 2-5 miles of the burglar's own home: again, opportunism. Petty opportunist criminals tend to live on poor estates (only very successful criminals live in affluence). As such the target of opportunistic burglaries tend to be other poor estate homes, where the pickings are very slim. Dumb, petty opportunist criminals also have little knowledge of what is truly valuable, and are interested only in items that are easily fenced. Expensive jewelry is distinctive and thus hard to fence. Art and clothes are not very popular and hard to fence. Consumer electronics and tools are good, but ubiquitous and a fence will pay little for those (and a big screen TV is really awkward to carry). Money is paydirt, but who has several thou lying about in the house? Passports, credit cards and ID are good, but again, to turn these into good profit often requires specialist connections. And a petty criminal will not have those.