I may have an old schematic in Fritzing, but i doubt it. I never got around to documenting it, but it's simple enough. My Macbook developed a "hunchback" and i

I may have an old schematic in Fritzing, but i doubt it. I never got around to documenting it, but it's simple enough. My Macbook developed a "hunchback" and is currently having it's battery replaced, so i can't check the details. IIRC, i wired the relay to a default off, and there's button wired to the arduino that needs to be pushed before it turns on the relay. It then stays that way until one of the MQ-2 or DS18B20 sensors detect a reading that's outside normal operating parameters, or power is cycled. I spent quite a few hours fine tuning the MQ-2 with cigarette smoke, vape "smoke", and finally burning filament. The bad news is that the MQ-2 is rather cheap, so they need a long "burn in" period before they start giving even remotely consistent readings, and then they still vary wildly from each other. Once burn in is over though, they're rather consistent with their own readings, just don't try to match them to the neighbor :) As for the extinguisher balls, i considered it, but they looked like they'd probably destroy more than they would save. I keep my printers on floor tiles, ~60cm away from any wall, and with 160cm to the ceiling, so any small fire would have trouble spreading. If the fire was to spread beyond that, i doubt the fire extinguisher balls could save it. I was looking into CO2 cannisters, but couldn't find any that could be activated by an electrical circuit, and while i could probably design a mechanical part to activate a regular fire extinguisher, i'm not sure i would trust it.