1. A device for estimating a core body temperature of a user, the device comprising: a heat trap shaped to receive a liquid stream and contain the thermal energy therein; said heat trap comprising low thermally conductive material; a temperature sensor in communication with a microprocessor, said temperature sensor associated with said heat trap and disposed proximate a surface of said heat trap, wherein said liquid stream is directed across said temperature sensor; wherein said heat trap comprises a sidewall including an upper section having an opening and a lower section having an outlet, said sidewall defining a perimeter around an enclosing the region, said enclosed region defining a passage for said liquid stream; and wherein said opening has a greater width than said outlet.