Klix (TM Outdoor Ultrasonic Bark Control Birdhouse - Anti Bark Off Limiter Birdhouse Box Silencer Controller Device for Pets (Yellow) Safe and effective for all size and breeds of dogs.This device with battery operated 4 sensitivity settings to indicate what barking level activates the unit Detects barks up to 50 feet with the use of an internal microphone Uses ultrasonic sound to deter unwanted barking ,Durable and weatherproof for outdoor use it can be placed in a tree, hanging from a pole, on a fence post, etc. for best results, the area between the outdoor bark control and the dog should be free of any obstacles