Autonomous photoelectric smoke sensor. When a fire hazard is detected, the red alarm light starts flashing and a strong sound signal is emitted (volume up to 85dB). The non-replaceable 3V battery lasts up to 10 m (characterized by low energy consumption), when the battery is low, a warning signal is activated, which is repeated every 53 seconds. The sensor has a function test button to check whether it is functioning properly.