Abstract. It is demonstrated how a commercially available MEMS thermopile infrared radiation sensor can be used as thermal conductivity gas detector (TCD). Since a TCD requires a heater while IR-thermopile sensors have no integrated heater, the thermopile itself is used as heater and temperature sensor at the same time. It is exposed to the measured gas environment in its housing. It is shown that, by using a simple driving circuitry, a mass-produced low-cost IR sensor can be used for hydrogen detection in applications such as hydrogen safety and smart gas metering. The sensor was tested to measure hydrogen in nitrogen with concentration of 0–100 % with a noise equivalent concentration of 3.7 ppm.