In one embodiment a temperature sensor system includes two sensor assemblies with different thermal resistances, each sensor assembly including a temperature sensing portion and a thermoelectric generator portion configured to receive heat flow from a body through the associated temperature sensing portion. A control unit is operably connected to the sensor assemblies and the memory. The control unit is configured to execute program instructions stored in the memory to obtain signals from the temperature sensor portions and the thermoelectric generator portions and to calculate and output a body core temperature (TB) based upon the obtained signals.