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.
Train whistle
North American steam locomotive whistles have different sounds from one another. They come in many forms, from tiny little single-note shriekers (called "banshees" on the Pennsylvania Railroad) to larger plain whistles with deeper tones (a deep, plain train whistle is the "hooter" of the Norfolk & Western, used on their A- and Y-class Mallet locomotives). Even more well known were the multi-chime train whistles. Nathan of New York copied and improved Casey Jones's boiler-tube chime whistle by casting the six chambers into a single bell, with open "steps" on top to save on casting. This whistle is still considered the "king of train whistles". It is the most copied train whistle in the United States, and many railroads' shops cast their own version of it.