The unit is a photoelectric smoke alarm device. 

A DC 3V not replaceable lithium battery and warns you when the battery is low.

In order to not disturb your rest, the product is designed with silence function and no disturb function.

With the increase of working time, the alarm detection signal will be decayed. When attenuate to the certain value, the alarm will send a fault signal to warn you to replace the product immediately.

The product is designed with the test function by pressing the test button, which is used to test to assure the product working normal. Weekly testing one time is required.