HQ Inc. offers the CorTemp temperature pill that can record body temperature and heart rate data continuously and wirelessly transmit this data to an external device for graphing and archiving. The pill is swallowed by the participant and records data as it passes through the intestines before eventually being excreted by the human body hours later. The pill has seen many applications in the real world for athletics, for the military, for monitoring of animal vitals.
This article from ieee documents how football teams are using the pill to monitor players who may be in danger of dying from overheating during intense physical drills, which sadly happened to Korey Stringer in 2003.