In this work, we present a low cost multi gas detection system for a simultaneous measurement of up to four kinds of gases. The main conclusions are based on the investigation of CO 2 gas concentration, which are also supported by CH 4 gas and H 2 O vapor. It was found that the continuous heating of the IR source and the absolute values of thermopile voltages are not suitable parameters for the gas detection because of high sensitivity to the influence of temperature and/or gas flow parameters. The sine like signal is preferential for our measurement system. The amplitude of the sine is very stable and is proportional only to the concentration of particular gas (according to the optical filter) and is not dependent on the concentration of other gases or on temperature. In this way, the CO 2 gas concentration can be measured from 50 ppm to 400 000 ppm with the same measurement setup. However, the lower detectable concentration of CH 4 was about 500 ppm.