Functional Tattoos:

"Diabetics monitoring their glucose levels may soon put the days of painful finger-sticks behind them. Instead, they can go through the one-time ordeal of getting inked with a nanoparticle tattoo. Heather Clark, a scientist at Draper Laboratories, has developed a nano ink particle that constantly samples glucose levels in the skin. Injected subcutaneously, the ink changes color in response to glucose content."
If this really works, I will get it done.

via neatorama.com

(Click on the pic for more info!)