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.
History of the Metropolitan Police Service
From the Metropolitan Police's foundation, the force had relied on the use of hand rattles for officers to signal the need for assistance. In 1884 the Home Secretary invited competition from many companies to invent a "police whistle" to replace the rattle. J.Hudson & Company of Birmingham were awarded the contract for 7,175 whistles at the price of 11d each. At the same time, a competition for the contract to supply the Metropolitan Police with new truncheons was under way. This contract was won by Ross & Company, who supplied the Metropolitan Police with Lignum vitae truncheons. In 1886, during a riot between warring working parties in Hyde Park, many truncheons were damaged or broken, samples were sent off to be tested by the Royal Army Clothing Department, at a cost of 16 shillings per day. In October 1886, 900 pounds worth of Lance and Cocuswood were purchased, to use in place of Lignum vitae that was deemed unsuitable after Army testing.