From Danger Room:

In its ongoing quest to measure every aspect of U.S. troops’ physiology, the Pentagon’s esoteric research enclave wants to develop a durable, unobtrusive device that can track the body’s physical response to stress. Military scientists believe that using the device — preferably a tattoo — to track heart-rate, temperature or bio-electric response during various training situations will help them crack the code of combat fatigue.

Darpa, the same guys who are working on robot ostriches, battlefield illusions and a texting spy camera, recently requested research proposals to develop the next generation of bio-statistic devices. The solicitation, which opened last month, hopes new technologies can transcend the current paradigm of patient monitoring of needles, gels and electrodes. And advanced materials make it possible to integrate everything from the sensors to the transmitter into thumb-sized membranes that can stick to skin — like temporary tattoos.

Full Story: Wired Danger Room: Pentagon’s Mad Scientists Want a Tattoo That Tracks Troops’ Vitals

See also: Electronic Sensors Printed Directly on the Skin

This makes a lot of sense to me. I recently tried out a BodyMedia arm band, but returned it because it was a bit too big to wear day to day (it wouldn’t be bad for wearing just during workouts though). But a temporary tattoo that could track much of the same stats would solve the bulk/appearance problem without having to resort to, y’know, implants.