PetSafe Outdoor Bark Control. Ultrasonic outdoor bark control unit looks like an ordinary birdhouse that can hang in a tree, on a fence post, or anywhere outside. Detects barking up to 50' away & has 3 range settings. Whenever your dog - or your neighborʼs - barks, he will hear a safe, high pitched sound (inaudible to humans) that will teach him to stop his annoying habit. Max. range: Up to 50'. 4 levels of operation including test mode. Durable & weatherproof. 2-color LED for good/low battery indication. Powered by 9 volt alkaline battery (not included).