Scientists have developed a new type of tattoo that is more useful than just showing off your personal identity. This special tattoo is a form of biobattery, or sensor, which can be implanted into your skin to monitor your progress during exercise — and also power electronic devices.

Currently, professional athletes pay close attention to a certain element in their sweat and blood called lactate. The more intensely you work out, the more lactate your sweat produces. This is due to a process called glycolysis, which occurs during intense exercise when the body needs to create more energy and lactate. “Lactate is a very important indicator of how you are doing during exercise,” study author Wenzhao Jia said in the press release. Monitoring your lactate levels is often intrusive, however, because you have to give blood samples at different times.

But the authors of the study, which was completed at the University of California, San Diego discovered an easier way to detect lactate: by imprinting a lactate sensor onto temporary tattoo paper. In addition to being able to monitor lactate levels, the neat little sensor is also able to strip electrons from lactate through the use of a certain enzyme — and then create a weak electrical current.

tattoo biobatteries A tattoo biosensor (enlarged above) detects lactate levels during exercise; a biobattery using the technology could power electronics.

“The current produced is not that high, but we are working on enhancing it so that eventually we could power some small electronic devices,” Jia, who is a postdoctoral student at UCSD, said in the press release. “Right now, we can get a maximum of 70 microWatts per cm2, but our electrodes are only 2 by 3 millimeters in size and generate about 4 microWatts — a bit small to generate enough power to run a watch, for example, which requires at least 10 microWatts. So besides working to get higher power, we also need to leverage electronics to store the generated current and make it sufficient for these requirements.”

The researchers studied the tattoo’s ability to generate power by placing it onto the arms of 10 healthy adults, all of whom were at different fitness levels. They made them exercise on stationary bikes, and found that people at lower fitness levels were actually able to produce more power. This most likely happened because people who were less fit were more apt to experience glycolysis sooner, since their bodies need energy sooner.

Though the energy produced from the devices wasn’t that powerful, the researchers hope that one day they might be able to power heart monitors, watches, and even smartphones from your sweat. Biobatteries are safer than regular batteries, since they don’t explode or leak toxins — and they’re also quicker to recharge.