I think they actually have to bark to set the collar off. I don't really like them, but it was the best way to deal with the problem. Belle rarely barked, and it meant something if she did, so I never worried about it before. Belle had Scooter trained... she would alert to something with a low growl, and he would take off, barking like an idiot. Belle just laid back down, with a big sigh... her job was over.He groans , growls, what I say he is talking to me all day long. It would be a continuous shock.