Horns are air-powered sound-making devices that allow diesel engines to warn people, animals and other chuggers, or to communicate with staff. The chuggers also commonly use them to greet other chuggers or people when passing by.
During the winter, chuggers are equipped with a snow horn and lantern to use in case they are to ever get lost in the snow or are in some form of trouble.
Whistles are the steam-powered equivalent used for steam locomotives and other kinds of machinery that are steam-powered.
Bells are used by a select few of chuggers such as Zephie. Chuggers like Piper and Decka are equipped with both a whistle/horn and a bell.
The various sounds for the horns, whistles and bells each individual chugger uses can be found on their individual articles.