A large breed dog such as a German Shepherd, Rottweiler, Doberman, Pit Bull, etc. that will foil an attempt to burglarize your house by making a chew toy out of said burglar. Ninety Nine times out of a hundred, the sight and sound of the four legged alarm system on the other side of the door would be more than enough to deter a potential burglar into looking elsewhere for an easy target. The four legged alarm system can also double as a car alarm as well personal protection against muggers and\or rapists while walking alone in the dark. Highly effective when the four legged alarm system is given a junkyard dog name such as "Scraps" or "Tiny".
I live in a crummy neighborhood but I've never been robbed since I've been here, because I have a four legged alarm system, a 130 pound German Shepherd that barks and growls fiercely at anyone with dark skin that walks by!