The MQ-137 is an Ammonia (NH₃) gas sensor from Winsen. The sensing element is SnO2, which has lower conductivity in clean air. When NH₃ (Ammonia) gas exists, the sensor’s conductivity gets higher as the gas concentration rises. A simple circuit makes measuring this change in conductivity and turning it into data fairly straightforward, but it does require some calibration. For easy Solderability, use our Gas Sensor Breakout Board. https://elecena.pl/product/17194929/ammonia-gas-sensor-mq-137 2020-09-25 https://elecena.pl/product/17194929/ammonia-gas-sensor-mq-137 2022-02-21 https://elecena.pl/product/17194929/ammonia-gas-sensor-mq-137 2025-04-11 https://elecena.pl/product/17194929/ammonia-gas-sensor-mq-137 2025-04-14