With respect to hackaday's Aging in Place theme, I think it would be quite possible to build a device that could monitor heart rate and body temperature and also be powered off the heat a body could produce. With microprocessors hitting nanoamp current draw in low power mode, it may be possible to power a circuit using a thermocouple and a body's temperature as the heat source. The thermocouple source input in itself could possibly be used to determine body temperature based on it's voltage change. A passive RFID chip with read/write capability could then be used to store current information that the processor has read from the sensors. In using RFID, the low power consumption point is addressed.

As we get older, our susceptibility to illness grows and a demand for more immediate response, a monitoring system like this could help detect changes in health that would require more immediate attention. An inexpensive, wearable, and no-batteries-required future.