Uses an old age principle of Negative Enforcement. Emits an ultrasonic noise every time it senses barking dogs. Controls device operates in a seemingly quiet manner to stop barking dogs. 50 ft. Detection Range. 40 Kilohertz Sound Transmission Range. Help control your dog's barking with the negative reinforcement of ultrasonic noise. Although the sound is quiet to humans, it is uncomfortable for dogs, who will quickly learn to stop barking when they hear the sound. The Super Bark Free is designed to emit noises every time it senses a dog's bark.