A lightweight, compact whistle, ideal for dog training, indoors or out. Ultrasonic whistles are particularly suited for training noise-sensitive breeds such as border collies. Although termed as a silent whistle, the whistle has to be slightly audible to the human ear, in order for you to be able to effectively control your dog as otherwise you would not be able to gauge the effect that it is having. Compact design. Adjustable pitch. Once adjusted please ensure the lock nut is fully tightened.