We describe herein a novel approach for visual indication of trace organic vapors. The sensor utilizes a microporous material within a visual thin film transducer to produce changes in color upon exposure to a very wide range of volatile organic compounds. Visual indication at 5 parts per million (ppm) is demonstrated, with optoelectronic detection achieved to below 50 parts per billion (ppb). Through a thoughtful design of the sensor, we are able to avoid interference from water vapor, a critical attribute needed for practical application.