French's "fil pilote" to control electrical radiators is quite bullet proof in this regard: No power on command wire = comfort thermostat, full power = "eco" t

French's "fil pilote" to control electrical radiators is quite bullet proof in this regard: No power on command wire = comfort thermostat, full power = "eco" thermostat, and there are other more convoluted signaling for various modes (send only positive voltage, only negative, only a third of the phase) , including simple anti freeze mode. There is an off command as well, but you really can't send it accidently. If your IoT dies, you'll most likely get to the comfort mode. Only nit is that in 2023 the default mode would probably be "eco" rather than "comfort"