This is the ultrasonic device that trains a dog to walk without pulling on their leash. It attaches between a lead and collar and emits a harmless ultrasonic tone that startles canines yet is inaudible to human ears. The dog associates the unpleasant sound with tugging on the leash, thereby learning to walk properly. The built-in speaker can be directed toward your dog to avoid disturbing other passing pets and it has four volume levels that can be adjusted to accommodate dogs with different levels of sensitivity. Compatible with any existing collar (not included) and leash (not included). Suitable for all dog breeds and sizes. Requires two AAA batteries.