The MQ-2 sensor is a very popular gas sensor for use with Arduino and other microcontroller boards, and is ideal for home gas or smoke detection projects, such as gas leak alarms.

MQ-2 is

The MQ-2 is a gas sensor that can detect many types of gases such as:

LPG (cooking gas)
Butane gas
Propane gas
Methane gas (CH₄)
Hydrogen gas (H₂)
Smoke
alcohol

Inside the sensor is a heating coil and a SnO₂ (tin dioxide) gas detector, whose resistance changes in the presence of gas in the air, allowing it to be converted to an electrical signal.

MQ-2 specifications

list	details
Supply voltage	5V DC
Electrical power	About 800mW
Signal type	Analog and digital (depending on module)
Warm-up time	About 20 seconds to 2 minutes
Detectable gases	LPG, Methane, Alcohol, Propane, Hydrogen, Smoke
Detection range	Approximately 300 - 10,000 ppm
Number of legs	4 legs (VCC, GND, AOUT, DOUT)

AOUT (Analog Out) – Analog signal indicating gas level. DOUT (Digital Out) – Digital signal (1 or 0) when gas level exceeds set point.

Using MQ-2 with Arduino

Wiring:

MQ-2 Pin	Arduino Pin
VCC	5V
GND	GND
AOUT	A0 (Analog)
DOUT	D2 (Digital) (if used)

Some MQ-2 modules have a potentiometer (adjuster) to set the threshold level on DOUT.

Example code for use in Analog:

int mq2Pin = A0;

void setup() { Serial.begin(9600); }

void loop() { int gasLevel = analogRead(mq2Pin); Serial.print("gasLevel: "); Serial.println(gasLevel); delay(1000); }

Example of code for Digital usage:

int mq2Digital = 2;

void setup() { pinMode(mq2Digital, INPUT); Serial.begin(9600); }

void loop() { int gasDetected = digitalRead(mq2Digital);

if (gasDetected == LOW) { Serial.println("gas detect!"); } else { Serial.println("Safe"); }

delay(1000); }