Acme Dog Whistle 535 nickel plated  Ref: 535

Many animals react differently to different whistles, each has different hearing abilities, but most animals hear quite clearly frequencies that defeat the human ear. The Acme Silent Dog Whistle produces ultra high frequencies in the range of 5800Hz. to 12400Hz. Used for training dolphins and killer whales at Sea World it is also famous for its effects on cats, horses, mice and even bats!