The PetSafe® Elite Outdoor Bark Control includes a digital timer that can be programmed to turn the unit on and off at specific times, just like an alarm clock. When the Elite Outdoor Bark Control is within range of barking, an internal microphone picks up the sound and the unit is activated. The unit emits an ultrasonic sound which cannot be heard by most humans, similar to a dog whistle. Startled by the high-pitched sound, the dog should associate his barking with the noise and stop barking. The attractive and discreet unit will look right at home anywhere in your yard, whether it’s hanging up or free-standing on a table or other area. With a range of 50 feet, the ultrasonic sound could cover a 1/4 acre yard.