Working Principle:uses ultrasonic sound to deter unwanted barking from either your or your neighbor's dogs. Effective: The barking stop device is effective with a range of 50 feet,detects dog barks up to 50 feet with 4 levels of operation including a test mode. Safety: The ultrasonic frequency is inaudible to human no harm to your family and pets completely which is totally safe to use. Durable: birdhouse shape and sturdy, waterproof is great for outdoor use, also easy to hang or set on a tree, wall or fence post, please make sure put the microphone less than 5 feet high and face the direction of the barking dog. Guarantee: Suitable for all breeds and sizes of dogs,except for deaf or hearing impaired dogs. 100% Satisfaction Guarantee,any problem, please do not hesitate to contact us and we will solve the problem for you 24/7.