What is the name of the device used by early firefighters that now appears on firefighters' badges and helmets?

The device used by early firefighters that now appears on their badges and helmets is known as a bugle. Historically, a bugle was used as a means of communication to alert fire crews during emergencies, signaling important instructions or calls to action. This instrument was practical in the chaotic environment of fire scenarios, allowing commands and alerts to be transmitted over distances even when smoke or noise levels were high.

To this day, the image or representation of a bugle is often incorporated into firefighting insignia, symbolizing not just the rich traditions of the firefighting profession but also the importance of communication and teamwork in effectively addressing emergencies. This historical significance adds to the identity and pride of modern firefighters, connecting them to their predecessors who relied on such devices in life-saving missions.

Other options, such as megaphones, trumpets, and keys, do not have the same historical relevance to the traditions of firefighting as the bugle, making it the correct answer in this context.