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.
Whistle mix
A typical whistle mix is made from 70% potassium perchlorate and 30% sodium benzoate, measured by weight. The fuel in most whistle compositions is a salt of an organic acid. Compositions with chlorates and gallates were used historically, but have now been abandoned as prone to accidental ignition. These mixtures however, are less sensitive than the formerly used ones, which often contained mixtures with picric acid and potassium picrate.