Effectively deters barking when worn. When the microphone picks up the sound of your dogs 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.
"Does not work"
I bought 4 of these and my dogs still bark. They just ignore the sound. I see the red light go off when the bark, but they don't care.