The detector is a photo-detector that uses the most advanced optical sensing chamber. It is designed to provide open area protection without wiring, and it is easy to install and construct. The red indicator on the detector can provide visibility alarm in all directions. It flashes once every minute, indicating that the detector is working. When a fire alarm occurs, the indicator will be continuously lit until the smoke concentration is lower than the alarm threshold. When the battery is under low voltage, the indicator will flash and the buzzer will beep. The test button is used to test whether the detector works normally. Each time the button is pressed, the buzzer emits a beep, the red indicator flashes. And the button can be used for local mute during a fire.