Fritzing

Hooking up an MQ-2 (gas & smoke) sensor to an Arduino Uno via a breadboard

The wiring connection is important:

Both A pins and the left H pin need to be connected to 5V. Both B pins need to be connected to the analog input (A0). The right H pin needs to be connected to the ground (GND).

A load resistor from 2kOhm to 47kOhm needs to be connected to both the analog input and the ground. I am using a 22kOhm resistor here.