Ultrasonic Bark Deterrents. How do They Work ?

Ultrasonic bark control and deterrent devices use a high-pitched, ultrasonic sound to deter annoying barking. In some cases (some products), this works up to 50 feet away from the device. The device is activated by an internal microphone that picks up the sound of barking. An ultrasonic, high pitched sound is emited, which can only be heard by dogs. The dog is startled by the sound and associates their constant barking with the unpleasant noise.