The BS-657 detector is a visible smoke detector as well as a thermal detector. It was built to provide fast detection in case of fire. It consists of two parts. A plastic base mounted on the roof and the main body of the detector which fastens to the plastic base with a simple rotation to the right.
The smoke detector has an indicator LED that lights up continuously in case of fire detection, until
cancel command comes from the panel. The LED indicator also flashes every 4 sec as an indicator of good operation.