My sisters got my 87 year old Mom a gadget that sounds like a BIG dog barking. She can turn it off or on whenever she needs to. Last year some man cut the window screen on her back deck right outside her bedroom window. She hear it and thought it was a cat scratching. She saw man's shadow and told him he'd better get away- that the police were on the way. Lived by herself then but not now. He also had cut the bathroom screen.