With the technique of scattering, the detector's reliability, stability and consistency are improved. The special chamber design ensures the insert-defend, dirt-defend and anti-light disturbance. The detector is non-addressable and can start operation by applying DC power. It has a pair of output contact, which is broken in normal and closes and remains closed after alarming, and the indicator on the detector is lit. It can be reset after power cut. The detector adopts orientation base, with only one mounting mode.