What sound might indicate a fire in the APU?

A sounding horn is a specific auditory alert associated with certain emergency situations, including the possibility of a fire in the Auxiliary Power Unit (APU) of an aircraft. This type of sound is designed to quickly grab the attention of ground crew or ramp agents, signaling that an immediate assessment is needed. It's crucial for ramp agents to recognize this sound as a warning to investigate further for safety and troubleshooting.

Other types of alarms, like loud alarms or sirens, may be used in various contexts, and their meanings can vary depending on the specific equipment or aircraft. A continuous beep could suggest different issues or alerts unrelated to a fire. The clarity and distinctiveness of a sounding horn make it the most relevant choice for an indication of a fire in the APU, aligning with the protocols that prioritize safety and immediate action upon such warnings.