Due When sensor is exposed to hydrogen gas,due to adsoprtion of gas over the surface of sensor , redox reaction occur between hydrogen and oxyen gases leading to decrement in barrier height thus resulting in reduction in sensor resistance. We ought to design a sytem such that it generates a signal ( in the form of alarm or message ) when the concentration of Hydrogen gas increases from its critical value. In future, it can be extended to other gaeses like carbondioxide, methane, LPG etc.