fire and carbon monoxide alarms are critical since these emergencies aren't caused by burglars but by our own negligence or carelessness.
but, yeah, dogs and signs can be all that it takes to avoid burglary in your home. I even read a blog once that all he did was put some tattered boots and large dog dishes out on his porch, with a note to a friend saying how his dogs (and I doubt that he had even one) had attacked someone the other day and he has locked them up inside the house since he'll be out for a while. It was a great and successful bluff!
"L" ~ Home Security System