Shepherd's whistle
They are also produced commercially. Simple whistles may cost less than 1 USD in bulk; expensive ones may be quite ornate. They are commonly made of plastic, aluminum, stainless steel, silver, brass, titanium, Corian, jade, buffalo horn and other materials.
J Hudson &amp; Co
In 1883 Hudson began tinkering in his toolshed to make gadgets to sell, including whistles. After observing local police struggling to communicate with rattles, he realised that his whistle could be used as a tool. As the story goes, Hudson, a violin player, accidentally dropped his violin and it shattered on the floor. Observing how the discordant sound of the breaking strings travelled, Hudson had the idea to put a pea in the whistle. This gave it an ear splitting rattle that could grab attention even a mile away. After a demonstration at Scotland Yard, Hudson had his first sale.