MQ 2 gas sensor working

Hello,
I was wondering how exactly the gas sensor works, ie the detection process. I tried downloading datasheets from multiple web pages but none of them in general explain how exactly the sensor detects the presence of gas. It is known that the resistance of sensor changes when there is presence of gas, but I need a little more information on how exactly that change happens. Any inputs?

They work by current induced when the gas is ionised

http://www.engineersgarage.com/insight/how-gas-sensor-works

Thanks a lot mate!, appreciate the response. :slight_smile: