Steam whistles were louder and served both as warning and signaling devices. Bells on passenger trains were sounded for a short period before the train moved, the ringing continuing until the locomotive left the station. The bell was an indication that a train was either moving or about to move. The fireman usually controlled the bell, originally tugging on a cord to ring it, while later bells were actuated by air pressure, requiring the fireman or engineer only to turn a knob. Bells were also sounded in urban areas where the ringing bell could be heard long before the puffing steam engine.
Noise pollution makes bells less effective today.
Whistles served not only as a warning, but were a communications signal for train crews as well. Without radios, communications depended on hand and light signals, often answered by a locomotive whistle. Sometimes whistles served alone. Whistle signals sounded between locomotives and operators in depots, or to the flagman protecting the rear of a train. Only the engine's whistle had the volume to be heard long distances Different patterns of long and short tones had meanings.