Here I am presenting you a simple smoke sensing alarm circuit using 555 timer . By using this circuit you can detect smoke and it alarms when the air is contaminated. Let me introduce you the components used in it. IC- NE555 Time r Sensor- PHOTO INTERRUPTER MODULE SPEAKER This smoke detecting alarm is based directly on an astable multivibrator and sensor (Photo interrupter module). The sensing module triggers the oscillator and generates an alarm through the loud speaker. Read More.....