Weyers and Holler's trick is to 3-D print a "bump" key, which resembles a normal key but can open millions of locks with a carefully practiced rap on its head with a hammer. Using software they created called Photobump, the two engineers say it's now possible to easily bump open a wide range of locks using keys based on photographs of the locks' keyholes. And even without a high-quality 3-D printer, those specialized bump keys can be mail-ordered from 3-D printing services like Shapeways or i.Materialise that have no restrictions on printing keys.