Stop Nuisance Barking with the new PetSafe Outdoor Bark Control Birdhouse. This outdoor bark control unit was designed for easy hanging or mounting on a tree, wall or fence post to keep your own dog from barking, or either your neighbor's dog from barking. How does it work? When the Outdoor Bark Control Birdhouse unit is placed within range of a constant barking dog, an internal microphone detects the barking sounds and the unit is activated. The PetSafe Outdoor Bark Control Birdhouse unit emits an ultrasonic sound to stop dogs barking. The ultrasonic sound can only be heard by the dog. When the dog is startled by the high-pitched sound, it should stop barking as it will associate its bark with this unpleasant noise. The PetSafe Outdoor Bark Control unit has 4 settings which includes 3 Sensitivity Levels and a Test Mode. This unit is effective for bark control up to 50 feet. The PetSafe Outdoor Bark Control unit should be placed facing the barking dog and within fifty feet of the dog. This unit is designed with provisions for hanging or wall mounting and it should not be positioned any higher than 5 feet. For optimum bark control results, the area between where the Outdoor Bark Control unit is placed and where the dog is should be free of any large objects or obstacles. This unit is not recommended for indoor bark control.