Researchers from the Swiss Federal Laboratories for Materials Science and Technology, otherwise known as EMPA, have created an invisible keypad — for securing doors or safes from tampering and theft — using printable electronics.

To create the keypad, which is indiscernible to the naked eye, researchers printed electronic circuits and sensors composed of transparent conductive metal oxide ink onto a surface via inkjet printer.

Once printed, the circuits were annealed — or heat treated to alter the physical and, potentially, chemical properties of a material, thereby making it workable — on carrier foil that was dyed blue. Unlike transparent film, blue ink can absorb light, enabling it to be sintered onto the substrate via high-energy light irradiation. During this process, the blue tint disappeared while the optoelectrical characteristics of the transparent ink composed of indium tin oxide nanoparticles simultaneously improved.

Undetectable to the human eye, the sensor surfaces can be placed on panes of glass or curved door handles and can potentially be used to secure banks, hospitals and even private homes.

In the example depicted in the video provided by EMPA, researchers transformed the screws of a door hinge into invisible keypad buttons where a user enters a passcode to gain entry into the passcode-protected door. According to EMPA, the existence of the invisible keypad would be known only to the user and invisible to thieves.

For more information, watch the accompanying video or visit the EMPA website.