Train whistle

A train whistle or air whistle (originally referred to as a steam trumpet) is an audible signaling device on a steam locomotive used to warn that the train is approaching, and to communicate with rail workers.

The older steam whistles were almost always actuated with a pull cord (or sometimes a lever) that permitted proportional (tracker) action, so that some form of "expression" could be put into the sound. Many locomotive operators would have their own style of blowing the whistle, and it was often apparent who was operating the locomotive by the sound. Modern locomotives often make use of a pushbutton switch, which takes away the fine control over the way the whistle is sounded.