Lenggotong Portable Durable Training Ultrasonic Alloy Whistle Key Chain for Dogs The dog whistle sound includes 3 parts. 1.The Ultrasonic. Human's ear can not hear it, but dog can hear it. 2.These light sound can be heard by human, which help owner sound a long or short whistle to train them. 3.Adjustable pitch, simply tighten or loosen the screw to work out your dogs frequency.It should be noted that this whistle is audible to the human ear, essential for gauging its efficiency.