KEYS have been around for a long time. The earliest, made from wood, date back 4,000 years, to the ancient Egyptians. The Romans improved them a bit by making them from metal. But there, more or less, they have stayed. Electronic card-keys aside, a key is still, basically, a piece of metal sporting a series of grooves, teeth and indentations which, when inserted into a keyway, line up to move pins and levers to lock or unlock a mechanism.

Such keys are made with conventional manufacturing techniques, such as cutting and stamping. But now there is a new way, in the form of 3D printing, to craft metal objects. And keys are about to succumb to it, to the great benefit of keyholders.

A 3D printer works by melting together layers of material that are added successively to the object being created. It can thus make something from the inside out, as it were, by printing intricate internal features and then covering them with a solid layer. Features shielded from view are extremely difficult to copy, let alone reproduce using normal machine tools. What better way to reinvent the key, reckoned Alejandro Ojeda, a mechanical engineer who at the time was studying at the Swiss Federal Institute of Technology, in Zurich, than to 3D-print it in this way.

What prompted his interest is how simple it is to copy most keys: a few minutes at a local key shop will usually suffice. And copying is getting easier. It is now possible to take a picture of a key with a smartphone and turn the image into a computer file that can be used to make a replica with the aid of a cheap, hobbyist 3D printer. The resulting duplicate will probably be printed in plastic, and thus lack durability. But it is likely to be good enough to work at least once—and once might be enough.

Dr Ojeda’s answer is the Stealth Key (pictured). This is printed in titanium, one of the toughest of metals. Its teeth are hidden under a pair of narrow ledges, making it unscannable. But when inserted into the lock the teeth can operate the mechanism.

To bring the Stealth Key to market, Dr Ojeda teamed up with Felix Reinert, an expert on 3D-printing metal, to found a firm called UrbanAlps. Jiri Holda, a lock designer, joined them to help devise a keymaking process that employs an industrial 3D-printing system called selective laser melting (SLM). This is currently used to make high-strength components for jet engines and gas turbines. Indeed, it was these uses, which also involve printing a lot of concealed detail, that gave Dr Ojeda his key-printing idea in the first place.

SLM, as its name suggests, uses a laser to fuse the layers of metallic powder of which the object being printed is made. It is good at its job, but slow. It takes only seconds to cut a conventional key, but making a Stealth Key can occupy the best part of a day. UrbanAlps’ SLM machine does, however, print 850 of them at a time—each, naturally, different from the others.

Stealth keys are not cheap. A pair, together with a lock mechanism (made the conventional way), cost about $200. But UrbanAlps’ founders hope the added security they bring will make them attractive—probably to industrial customers to start with, and to the general public as padlocks. They do have a downside, though. If you lose one, getting a replacement will involve a security check, because only UrbanAlps has the digital-design file for the original. And a duplicate will take another day in the 3D printer.