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 Down the Wind (novel)
Whistle Down the Wind was a novella written by Mary Hayley Bell and illustrated by Owen Edwards. It was published in 1959 by Boardman and retailed for 12 shillings and sixpence (62½p). The central characters are three children — Swallow, Brat and Poor Baby. The story of the Great Secret is told by Brat.