When turned on, the battery operated device is triggered only when a dog barks. As a result, an ultrasonic wave released which quiets the down the dog. This wave is inaudible to humans but very noticeable to dogs. It serves only to interrupt the the dog's barking pattern. You see, when a dog is intently focused on whatever object is causing it to bark, the goal is to pry their attention away and they forget about the original stimulus. There are several ways to try and stop dog barking but the delivery of an ultrasonic wave is part of the genius of bark off.