Maybe it could be combined with thermostats? E.g. one for "if it ever gets hotter than N degrees, disconnect all heating elements and trigger some alarm", another one for "if it's warmer than X for longer than Y minutes, do the same". That could also be to the network, too, it just would never read from it, or from anything electronically. Just bimetals closing or opening circuits, basically. How expensive would that even be? (If you planned for it from day 1 of the design I mean, not retrofitting things)