Rice cookers (usually) make clever use of 1) alloys whose magnetism depends on temperature and 2) the fact that boiling water occurs at a fixed temperature. With a "trigger" temperature just above the boiling point of water, the rice cooker automatically turns off the heating element when all the water is gone (and thus the temperature starts to rise above boiling point).
Rice cookers (usually) make clever use of 1) alloys whose magnetism depends on temperature and 2) the fact that boiling water occurs at a fixed temperature. With a "trigger" temperature just above the boiling point of water, the rice cooker automatically turns off the heating element when all the water is gone (and thus the temperature starts to rise above boiling point).
More detail here: https://youtu.be/RSTNhvDGbYI