ACME 560 Thunderer roller whistle Used to make the dog sit (at a distance). Not affected by weather conditions. Vibration frequency of 4300 Hz. The plastic whistles from ACME work with numbers for different pitches. The advantage of this is when you have lost the whistle. You know by the number of the whistle which one you can best buy again. #VMmenu142 li.vmOpen>ul.menu{display: block;} #VM