Works by sending out an ultrasonic signal that only dogs can hear when activated by the barking. The ultrasonic sound is 100% harmless. Adjustable stretch collar to fit different sizes. Trigger accurately by bark vibration (cannot activate by other dogs' barking) train your dog to stop excessive barking easily and painlessly. The bark control collar is activated by a vibration sensor and microphone, this prevents unintentional corrections. It also ensures that the bark collar will only activate if the dog wearing the bark control collar starts barking or making other nuisance level noise, ensuring your dog is never confused by a correction occurring accidentally. Waterproof bark collar is the best for medium and large dogs of all temperament types, even stubborn breeds. With different modes of operation, you can find the best bark control option for your dog.