The PetSafe Ultrasonic Bark Control Collar effectively deters barking when it is worn. 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. Designed for dogs over 3.6 kg it will fit dogs with neck size up to 71cm. The water resistant, adjustable collar features a low battery indicator, on-off switch, two 3-Volt Lithium CR2032 Batteries and an operating guide.