The Ultrasonic Bark Control is great for curtailing the barking of small or timid dogs. Uses ultrasound to deter barking. Activated automatically by bark or manually by owner. Can be used as a table-top unit or hand-held. Has a 25 foot range. Note:Ultrasonic tone does not affect all pets the same way. Younger, smaller, high-strung dogs may not pay attention to it at all and respond better to another form of stimulation. The PBC-1000s LED light will glow red when the microphone picks up on the barking and the Ultrasonic tone is being given or the button is manually pressed.