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 along with the gas concentration rising. A simple circuit makes measuring this change in conductivity and turning it into data fairly straight-forward, but does require some calibration.
For easy Solderability; use our [Gas Sensor Breakout Board](https://www.sparkfun.com/products/8891).