Sensitive material of MQ-7 gas sensor is SnO2, which with lower conductivity in clean air. It make detection by method of cycle high and low temperature, and detect CO when low temperature (heated by 1.5V). Electronicstor.pk

MQ3 MQ 3 MQ-3 Alcohol Detector Gas Sensor Module is a simple to use MQ-3 Alcohol Detector Gas Sensor Module which can sense the presence of Alcohol in the air. The module uses our MQ-3 sensor. It simplifies the interface to the odd pin spacing of the sensor and provides an interface through standard 4 x 0.1″ header pins. It provides an analog output corresponding to the concentration of the gas in the air and an easy to use digital output. The onboard potentiometer can be used to set the maximum gas concentration beyond which the digital output gets triggered. Just power the module with 5V set the threshold and you can start getting the gas concentration of the air around the sensor! An onboard LED signals the presence of any gas. Perfect sensing alcohol concentration on your breath just likes common breathalyzer. mq3 alcohol sensor working