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.
Alfred De Courcy
Being a skilled metal worker, de Courcy was very creative in making new designs and registering new patents for whistle construction. He was in fact the only whistle maker beside Hudson to successfully cross the heights of Victorian era into World war I and onward.