This outdoor ultrasonic bark control device is designed to determine nuisance barking with a decorative touch.  Not recommended for indoor use or use with deaf or hearing impaired dogs.  Unit detects barking and sends the sonic signal up to 50 feet.  Safe and effective for all sizes and breeds of dog.  Powered by 9v battery, not supplied.  Unit appears new, in open box, listed as used because I cannot determine that it hasn't been.  But there are no visible signs of weather or wear on the unit.  Can be used for your dog, or set up near a neighbors dog who is a nuisance barker.  When the unit detects barking, it sends an ultrasonic signal that is unpleasant to a dog and cannot be heard by people.  The dog should eventually associate the unpleasant sound with the barking and reduce the barking frequency.