Easiest way to get this foolproof would be to put an induction loop around the power cable and use the reading from that as a proxy for on/off state. It would

Easiest way to get this foolproof would be to put an induction loop around the power cable and use the reading from that as a proxy for on/off state. It would catch any case where the stove is drawing power, irrespective of possible failure modes of the stove itself.