PetSafe Anti-sound device is used to curb excessive barking indoors with the help of harmonic tones. Anti-sound device that uses its internal microphone to pick up the sound when the dog barks and emits a tone that can be heard by the dog. The dog perceives the sound as uncomfortable and this then breaks the barking in most dogs.This tone is unpleasant but not dangerous to hearing. The dog will associate this with its barking and in time will stop its behaviour. The sound is not perceived by most humans.Facts about PetSafe Indoor Anti-Sound Device:Effective up to 8 meters.No collar needed.The anti-sound device is self-contained.Can also be attached to doors, windows and tables with adhesive tape.Fits dogs of all sizes.Water resistant.For indoor use only.Each unit requires 2 x CR2032 batteries which are included.