Researchers at the University Hospital of Bern, Switzerland, have adapted the 240-year-old technology behind self-winding watches for use in a pacemaker. In this case, the heart’s pumping motion does the winding.

Already tested in pigs, the miniature heart-powered device could eventually replace bulky batteries and “give the pacemaker the intrinsic ability to harvest energy continuously inside the body,” Andreas Haeberlin, a cardiologist and bioengineer at the University Hospital of Bern who collaborated on the project, told IEEE Spectrum.

Haeberlin and his colleagues took the self-winding mechanism from a wristwatch and replaced the oscillating weight with a smaller but heavier one made of platinum. They added a microgenerator from a quartz watch (to convert the mechanical energy to electrical energy) and then attached the device to a pacemaker, according to the technology magazine.

In a paper published last September, Haeberlin and his colleagues proposed including a small battery backup for reliability purposes. His and other research groups are also pursuing other methods of harvesting electrical energy from the body—with the goal of eliminating primary batteries in implanted medical devices.