Embedded piezoresistive microcantilever (EPM) sensors may be constructed for various sensing applications. In each application, a custom sensing material that responds volumetrically to the desired analyte is designed. Here, we constructed EPM sensors for chlorine gas (Cl2) detection. The sensing materials used consisted of polymer matrices combined with NaI crystals. Sensors constructed from a silicone-based matrix exhibited the strongest response to Cl2, with detection limits in an outdoor exposure setting of approximately 20 ppm.