A polyaniline–tungsten oxide hybrid nanocomposite with honeycomb type morphology was synthesized by in situ one pot chemical oxidative method and used for sulfur dioxide (SO₂) monitoring application for the first time. Using a cost-effective spin coating technique a sensing device was fabricated for the monitoring of SO₂ at levels as low as 5 ppm. The fabricated sensing device works at room temperature, which reduces its power consumption, cost and need for complex circuitry. It was found that the sensing response of the nanocomposite based sensing device (∼10.6%) is greatly enhanced as compared to that of its individual parent devices (∼4% for polyaniline nanofibres and is negligible for tungsten oxide nanostructures) for 10 ppm SO₂ at room temperature. The reason for this remarkable response has been discussed in light of several factors, such as optimum porosity, branched structure and formation of heterojunctions. In addition, the fabricated nanocomposite based sensor was found to be reliable in terms of stability, selectivity, response and recovery time, detection range and reproducibility. The mechanism of SO₂ sensing in the said composite is proposed and discussed in terms of the formation of heterojunctions and explained with an appropriate energy band diagram.