A secondary aim was to experiment with a distributed smoke / hydrocarbon sensor. This is still on the cards but has been deferred to some future time as we need to give further thought to power / operational execution.
The MQ2 smoke / hydrocarbon sensor has a 'heater' which needs to run for at least 3 minutes before values settle. The present design for the leaf nodes wakes up from deep sleep, reads sensors, performs an MQTT transaction over the radio and goes back to sleep within 30 seconds. Therefore using the MQ2 in the current configuration will impact on the amount of power used by the node.
For the MQ2 to be useful as some kind of fire alert sensor it would need to be checked continuously as well. Logging smoke/gas at (say) 15 minute intervals would be of academic interest in charting progression of dust / smoke from afar bushfires or pollution but less exciting.
Of course in-house smoke alarms can run off a 9V battery for years so there are ways and means of solving this problem, it just doesn't have to be done to meet the next video submission deadline.
We'll hopefully still put an MQ2 on the radio tower, given there will be sufficient power there, just to see how it works.