Molly McHugh writes with this story about sensors that can be attached to temporary tattoos to monitor various medical information. "The Center for Wearable Sensors at the University of California San Diego has been experimenting with attaching sensors to temporary tattoos in order to extract data from the body. The tattoos are worn exactly as a regular temporary tattoo would be worn. The sensors simply sit atop the skin without penetrating it and interact with Bluetooth or other wireless devices with a signal in order to send the data....A biofuel battery applied as a temporary tattoo converts sweat into energy, and a startup within the center has developed a strip that extracts data from sweat to explain how your body is reacting to certain types of exercise. Amay Bandodkar, a fourth year PhD student at UCSD, explains that the sensors are programmed to react to the amount of lactate the body produces."