Abstract: Wearable devices capable of measuring a core body temperature and other vital signs of a user in a range of situations are described herein. The wearable device is arranged to be retained within the ear canal of the ear, in order to prevent the wearable device from inadvertently removing itself from the ear. Providing an infrared thermopile at the innermost end of the ear insert ensures that the infrared thermopile is provided as close as possible to the tympanic membrane which will be used to provide an indication of the core body temperature.

Abstract: A hydration monitor includes a temperature sensor (20; 65) for measuring a subject's core body temperature and a processor (30). The processor is arranged to accept measurements from the temperature sensor (20; 65) and calculate a hydration level in dependence on changes in the measured core body temperature.