According to NFPA 72, what type of signal must a smoke duct detector generate by default?

A smoke duct detector is designed to monitor air flowing through ducts for smoke presence, and according to NFPA 72, it must generate a supervisory signal by default. This supervisory signal indicates that the detector is functioning effectively and ensuring the safety of the ventilation system.

The supervisory signal serves to alert system operators of the status of the detection device without indicating an immediate need for an alarm response. This allows for proactive measures to maintain system integrity and ensures that any potential issues are addressed before they escalate into an alarm situation.

In systems where air quality and safety are of paramount importance, supervisory signals play a critical role by providing ongoing oversight without triggering unnecessary alarms for conditions that may not require an immediate emergency response.