Smoke particles and heat will be generated in fire , conventional fire detectors detect fire just by these physical effects. But the measurement of physical parameters is not enough for an early fire detection. Nowadays another method has been an area of major interest for early fire dtection which make use of the gases (for example CO) generated from combustion process to detect fire. A majority of existing gas sensors are not good for a early fire detection because of their low sensitivity. A detection method for measuring the gas concentration based on photoacoustic principle is reported in this work, which increased the sensitivity enomously. The rate of false alarm is decreased greatly also by combining carbon monoxide detection with carbon dioxide detection.