This started as a conversation about machines left running overnight and the associated risks. My machine is pretty much exclusively run unattended overnight and although it's in an outbuilding I started to wonder if there was a fire (or at least lots of smoke damage) risk from leaving it unattended. I still think the risks are pretty low, but for the sake of a smoke alarm and a few bits of electronics I had kicking about I thought it might be fun to build a fire alarm cutout device. Pretty much this device will sit inline and powered by the mains lead going to the BigBox. A standard smoke alarm with a relay output triggers the device to cut power to the printer via a spark-less solid-state relay. You can use either the type of low voltage smoke alarm designed to be interconnected (as per the box in the picture I'll attach in a moment) or if you prefer you could use a smoke sensor designed for a fire alarm panel. It also doubles up as a standard smoke alarm when the BigBox isn't in use and as a more convenient to access power switch/emergency shutdown button. Life keeps getting in the way so progress is glacial...So far I have built a little Bistable switch on a front panel PCB, mounted a little off the shelf 12v PSU and found a suitable off the shelf relay and smoke alarm. The bistable switch uses a 555, but if you want to build it out of a few transistors (or even one transistor if you are clever) instead that would do equally well, I just happen to have 555's kicking around with no use for them at the moment so I used a 555 Diagrams and a printable case design will appear once I have it finished and all working well. Usual caveats about working with Mains voltages apply.