PetSafe Ultrasonic Dog Remote Trainer BlackCollarless Ultrasonic Remote Trainer takes advantage of your pets sensitive hearing with a sound that is beyond the range of humans. When the system emits its ultrasonic sound, your furry friend will understand that you want him to stop whatever he is doing. The system also has a positive tone to reward good behaviors as well as a negative tone to counter undesirable ones. Features: For dogs of any size. Ultrasonic sound only your dog can hear.