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. Modern locomotives primarily use a powerful air horn instead of a whistle as an audible warning device. Tuttavia, whistle continues to be used by railroaders in the context of audible signaling, cum'è “whistling off” when a train gets underway.