What is the third type of fire alarm signal used alongside supervisory and alarm signals?

The third type of fire alarm signal, in addition to supervisory and alarm signals, is indeed a trouble signal. Trouble signals are critical in the operation of a fire alarm system as they indicate a malfunction or issue within the system itself, such as a disconnection, a low battery, or a failure in the wiring. This type of signal does not indicate an active fire threat but serves as an alert to maintenance personnel that there is a problem that could prevent the alarm system from functioning effectively in an emergency.

Understanding the role of trouble signals is essential for ensuring that fire alarm systems remain operational and ready to respond in the event of a fire. The timely identification of trouble conditions can help prevent false alarms and ensure that the system is adequately maintained, ultimately enhancing safety for building occupants.

The other options do not represent recognized categories of fire alarm signals within standard fire alarm system operations, which is why they do not fit in this context.