what to do during fire incident happens?
You could just mount the laser lights that a garage door opener uses as a safety device across an appropriate space, and connect the output to a buzzer. It will need power, of course.
Americium-241 in a smoke detector emits ionizing radiation in the form of alpha particles into an ionization chamber open to the air and a sealed reference chamber. The air molecules in the chamber become ionized and these ions allow passage of a small electric current between charged electrodes in the chamber. If any smoke particles pass into the chamber the ions will attach to the particles and so will be less able to carry the current. An electronic circuit detects the current drop, and sounds the alarm. That is from pedia, the video on YouTube is pretty good.
