It seems like some researchers from Radbound University in The Netherlands took advantage of the recent Four Days Marches of Nijmegen walking race for a little experiment earlier this month, where they convinced ten volunteers to swallow an RFID
pill as part of a study to monitor body temperature. Apparently, the pills recorded and transmitted the walkers' core temperature to a receiver in their backpack every ten seconds, which in turn sent the data via Bluetooth to a GPS-enabled phone that then relayed it to the operations center at Radbound. With all that info at their disposal, the researchers were able to monitor each walker and alert them if their temperature was reaching a dangerous level, or even alert others nearby if they weren't responding (which apparently wasn't necessary). As you might have guessed, the researchers are already hard at work planning an even larger test for next year's event, which they hope could eventually lead to the system being used at marathons and other sports events.