There are several different signals on the smoke sensors. The most common are flashing lights on the ring around the button, but can also be combined with sound signals.
Short flash: Sending signal. This means that it sends a message to the central. This is completely normal and will happen several times a day.
Short flash with beep: The sensor is calibrating.
|Rapid flash: Alarm signal.|
|Flashes every second: Silent alarm.|
|Flashes every 2 seconds: During warm-up and calibration.|
|Flashes every second: Calibration failed.|
|Flashes every 5 seconds: Self-diagnosis failed.|
|Flashes and beeps every 45 seconds: Low battery.|
Flashes every 4 seconds: Critical low battery, replace immediately.