The Ancol Constant Whistle is an important tool for any serious dog trainer. This whistle has the same frequency regardless of how hard it is blown. Whistles are wonderful training tools for dogs for several reasons. Firstly, whistles can be heard more clearly than the human voice, particularly on windy days. Unlike the human voice, the whistle will not convey panic, frustration or weariness and so sends an unambiguous signal your dog will not struggle to understand.