Systems and methods are disclosed for regulating body temperature. The system includes a housing that comprises compartments for a phase change material and a heat transfer material. The compartments are configured to transfer heat from the heat transfer material to the phase change material. A temperature sensor is used to determine when the phase change material has reached a pre-determined temperature. When the pre-determined temperature is reached, a release mechanism or lever is coupled to the temperature sensor to separate the phase change material compartment from the heat transfer material compartment or to remove the heat transfer material away from the phase change material compartment. The heated phase change material compartment can be used to regulate body temperature.