Is there any way to tell if an MQ-2 sensor breakout board is connected (and functional)? Readings from a pin with nothing attached look pretty much like readings from a pin with an MQ-2 attached! I was hoping to see some difference that could be used to differentiate an absent sensor from a connected sensor. Additionally, it would be nice to know that the sensor is functioning?
You have a pull-down (load) resistor in the circuit. Move that to the Arduino end of the wire so an open connection would read 0V.
Use two temperature sensors to be sure the heater in the sensor is working and heating the sensor above ambient.