Boatswain's pipe

A boatswain's pipe or boatswain's whistle (pronounced "Bosun") is a whistle that is made of a tube that directs air over a grape-sized metal sphere with a hole cut in the top. The players hand holds the sounding chamber and causes a change in the pitch by opening and closing the hand.

The historical use of the boatswain's pipe was as a signaling device on a ship. Because of its high pitch, it could be heard over the activities of the crew and bad weather.