The PetSafe PBC-1000 Bark Controller is an easy to use table-top unit to stop dog barking. The unit is activated by dog's barking. Once activated, the unit emits a "loud" ultrasonic tone that only your dog can hear. This unpleasant sound will surprise your dog and your will quickly associate the barking with the unpleasant noise and greatly reduce his barking. PetSafe PBC-1000 Bark Control Features: Uses ultrasound to deter barking Activated automatically by bark or manually by owner No receiver collar needed Table-top or hand-held devise Uses a 9-volt alkaline battery (not included)