MQ gas sensors are relatively cheap and are available for very many gas types. The serial code written on the ring of the sensor, in the illustrated image, MQ-5, gives away the type of gas that the MQ sensor can sense.

The major benefit of MQ sensors is that they are extremely cheap relative to what they provide. However, the main downsides is that MQ sensors actually expect the user to calibrate the sensor and the other is that the sensor needs a long time to initialize (even up to 24 hours for some gas types). Perhaps the calibration is the killer because calibrating means that the user is supposed to have an echelon to be able to compare the readings in order to change the sensitivity of the MQ sensor to match. The former would imply not only having access to a gas source, but also having the capability to diffuse the gas in measurable quantities in order to be able to perform measurements and then scale the sensitivity of the MQ sensor.

MQ sensors are thereby more practical where accurate measurements are not required and perhaps could be used only via their digital output, in the sense that they would detect whether there is some gas or not, however MQ sensors are not really designed for precision and the numbers obtained via the analog reading cannot really be converted to any physically meaningful values (such as or ) unless, of course, there is a calibration phase. Fortunately, there are sensors out there, just a little more expensive that are pre-calibrated such that the reading can be converted to something that is a scientific measure.