This smoke detector works according to the scatter-light principle. Even a small quantity of smoke particles is enough to trigger a loud warning tone (85 d B/3 m) & an optical alarm display (via LED). A practical test feature allows simple, easy testing of the entire device (including smoke chamber), a battery insertion security device ensures that the device cannot be installed without a battery. A total of up to 30 of these smoke testers can be connected together. If one detector is triggered, all the others will also sound to cover the entire premises. Simple mounting