PetSafe Collarless Outdoor Bark Deterrent. This birdhouse-shaped device provides ultrasonic correction to deter outdoor dogs from barking. Whenever your dog (or your neighbor's dog) barks, he will hear a safe, but annoying ultrasonic sound that's inaudible to humans. As soon as he stops barking, the ultrasonic sound stops, teaching the dog not to bark. With one correction level and three range settings, it effectively works up to 50 feet away. Its waterproof design ensures durability, and it operates on a 9V battery (not included). Hang it anywhere for convenient use and peace of mind.