The PetSafe Outdoor Bark Control device works in a similar fashion to that of a dog whistle in that it produces a tone that is inaudible to humans but dogs can hear it clearly and in this case is a nuisance to them to cease barking. As long as the pet continues its barking the tone will constantly be emitted. This is so that the pet will learn the connection between the two and will end its barking. There are 3 different sensitivity levels and a 50 foot range making it useful even if you are not the dog’s owner, simply place the device near enough that the dog is in range and now your neighbor’s pet will be nice and quiet.