The gas sensor will detect the level of leakage gas and show message according to that to display e.g. Low, Med, High and if the intensity is very high then it shows the Exit message on display. The LDR / PHOTORESISTOR works on intensity of light at night bulb is automatically turned ON and At the day bulb is Turned OFF. And the main thing is that the Fan and light circuit is active only when some one is inside the room or some one is in front of PIR sensor