The recent standard for measuring core body temperature during WBH procedures is the use of an indwelling rectal thermometer to constantly monitor the temperature for safety and for research reasons. Experiences from different clinics and research groups, including ours, show a high drop-out rate of potential study participants and patients, because of the discomfort of self-inserting a rectal thermometer for the treatment in a Whole-Body Hyperthermia. A wireless and reliable measuring technology would open this treatment for participants, who are declining their participation due to the indwelling thermometer. This device will exit the subject's body via bowel movement 1-5 days following ingestion and will not be reused.