Motion activated alarm that barks like a dog? Fun when guests come to your house too.
Way back, had a shelter dog which was very skittish about sudden noises. She got into the garbage one day when home alone, ate a pile of chicken bones, and caused a big vet bill. My girlfriend had a ton of Halloween decorations, including a doormat which screamed when someone stepped on it. "Hmmm, I bet if..." The dog touched the mat
once and never went near the garbage again. I did feel bad about how long she hid in the closet afterward but not yes-more-vet-bills-please bad.