||Colorimetric gas sensor system has been developed to identify the presence of toxic gases. The commercially available sensing system employs electrochemical cell, which are expensive, and demands bulky auxiliary instruments and high power consumption. To overcome these drawbacks of the existing technology, we have developed colorimetric sensors for detecting toxic gases such as HF, HCl, HBr2. We demonstrate that our dye systems are highly sensitive and selective. As an important application of our sensor system, we selected dipyrrole based organic molecules. The chemosensor is used to develop a test paper for detection of methylamine gas in the solid state.