Train whistle

A train whistle or air whistle (originally referred to as a train trumpet or air trumpet) is an audible signaling device on a railway locomotive, used to warn that the train is approaching, and to communicate with rail workers. Steam whistles were commonly used on steam locomotives, and were replaced with air horns on diesel and electric locomotives. However, the word whistle continues to be used by railroaders in referring to such signaling practices as "whistling off" (sounding the horn when a train gets underway).