The automatic power-off function of an automatic electric kettle is generally realized by a bimetallic thermostat located at the upper part of the water cup and inside the handle (or at the bottom of the cup, which requires a long air duct). There is no relay or thermistor inside, and it feels the temperature of steam released by water, so it is indirect. Generally, only after the water boils can the steam temperature reach the disconnection point of the thermostat. So, if you open the lid to boil water, it won't automatically disconnect.

Moreover, the water will not be automatically reheated after boiling (thermistor can't do it) because there is a linkage mechanism.

The temperature control and anti-dry burning parts of automatic electric kettle are patented products of a British company, which contain many precise details and know-how.