This is a commonly used gas sensor module kit that contains the most popular smoke sensor MQ-2, an alcohol sensor MQ3 and a carbon monoxide sensor.
MQ-2:
- Type: Smoke Sensor
- Detection Target: Liquefied petroleum gas, natural gas, coal gas, smoke
- Effect: it can be used to detect smoke or combustible gas concentration, applied alarms
- Operating voltage: 5V
- Analog output AO: the higher the concentration of combustible gas, the higher the output voltage
- Digital output DO: Adjustable concentration alarms by potentiometer, when the concentration exceeds the threshold you set, it outputs low level, otherwise high level output, and it can be connected to microcontroller or relay modules.

MQ-3:
- Type: Alcohol Sensor
- Detection Target: alcohol
- Effect: it can be used to detect the concentration of ethanol vapor, used in police alcohol measuring device
- Operating voltage: 5V
- Analog output AO: Adjustable concentration alarms by potentiometer, when the concentration exceeds the threshold you set, it outputs low level, otherwise high level output, and it can be connected to microcontroller or relay modules.

MQ-7:
- Type: Carbon Monoxide Sensor
- Detection Target: carbon monoxide or other gases containing carbon monoxide
- Function: used to detect the concentration of carbon monoxide, it can be applied to coal gas poisoning alarm device
- Operating voltage: 5V
- Analog output AO: the higher the concentration of carbon monoxide, the higher the output voltage
- Digital output DO: Adjustable concentration alarms by potentiometer, when the concentration exceeds the threshold you set, it outputs low level, otherwise high level output, and it can be connected to microcontroller or relay modules.