Flame failure devices

Tahiri was thinking very hard :

All of, twin oven, hob, plus those in the caravan - use constant spark when the button is pressed to ignite. Then then use a tiny thermocouple to sense that the have lit, to maintain the gas on. All can be lit with a match if necessary.

Our gas heating boiler and the caravan fridge on gas, plus water heater when on gas, again use electric spark ignition, but the flame is sensed not by thermocouple, but by a voltage generated by an electrode in the flame.

Doesn't quite answer your question though, but others might be able to add to the picture.

All that I've seen use a thermocouple to keep the gas valve open. This doesn't need an electricity supply - the thermocouple generates the electricity needed from the flame heat.

A method that's used in boilers with non-permanent pilot lights is that an electrode in a flame acts as a rectifier, and this is monitored. Often it's also used as the ignition electrode. Never seen this on cookers, and it wouldn't work without an electicity supply.