Dirty Smoke Detectos and Addressable Panels

Today after school I saw the facility manager take off the head from one of the smoke detectors in my school, blow compressed air into it, and put it back. He did that for only one smoke detector, which leads me to the question: If a smoke detector is dirty, does it let the panel know that it is, and how does it know?

A lot of panels do tell you. Sometimes it’s an elapsed time that determines when it might be dirty and sometimes it can tell over an extended period of time a % obscurity and when it crosses a certain threshold the detector is considered dirty.