We have these - but they're pretty useless to be honest. The worst they could do if someone entered the house would be to get all excited and pee on the floor.
They're more my wife's pets. I'll stick with cats or big, less needy dogs if I ever have the opportunity.
Fortunately, we live in a rather quiet neighbourhood and we're surrounded by very friendly people, a lot of them retired. The lady next door is a former vet tech and 3 of our cats spend all their time in her back yard - she spoils them rotten. And us too. She always brings us turkey and ham for Thanksgiving and little cakes for Christmas. The loveliest neighbour I've ever had.