A pair of young inventors in Hong Kong has developed a doorknob-replacing device to change the way we approach hygiene, their prototype successfully eliminating 99.8% of germs on contact using metal and light – a perfect solution for that perpetually tricky question of how best to exit a public restroom.

Sun Ming (Simon) Wong and 18-year-old King Pong (Michael) Li built their creation out of relatively straightforward materials: a cheap embedded ultraviolet LED light coupled with bacteria-killing titanium oxide.Even more ingenious, no external power source is required – the kinetic energy of the door’s motion is converted by a power-generating gearbox into the requisite juice to turn on the handle. Set inside a clear glass container bracketed by metal, the light activates the titanium oxide and turns on the germ-assassinating machine as you use it, after which it turns back off automatically. While similar processes have been used for a long time to disinfect surfaces, this solution is cheap and can be deployed on a massive scale for everyday use.

“Titanium dioxide kills bacteria best when lit by ultraviolet (UV) light, says Simon. UV wavelengths are among those in sunlight. But indoor handles and any used at night would have little natural exposure to UV light. So the teens are lighting their door handle from within. Now, every part of the coated handle will see UV light. To make sure the interior light reaches the coated surface, the teens fashioned their door handle from a long cylinder of clear glass. Each end fits into a bracket. Inside one of the brackets is a strong light-emitting diode (LED). It emits UV light. (Transmitting the light from one end of the handle to the other is similar to the transmission of light through a fiber-optic cable. In this case, though, the glass handle is fat rather than super-thin.)”