When the microphone picks up the sound of your dog's bark, the unit emits an ultrasonic tone that can be heard by your dog, but is silent to most humans. Startled by the high-pitched tone, the dog should stop barking, as it will associate its bark with this unpleasant noise. Features: Water Resistant Includes: 2 Indoor Bark Control units, 2 Adhesive-backed hook and loop fasteners, 4 CR2032 batteries, Operating guide, and a 1 year warranty Intended For: Dogs over 6 months of age Dimensions: L3.0XW6.25XH6.5 Weight: Weight .49 Caution: For comfort, safety and effectiveness of this product, please check your pet's reaction frequently. Read the Guide for this product carefully. If your dog exhibits improper behavior, discontinue its use immediately.