The current issue is because light is line-of-sight. Such systems traditionally need a lanyard of some kind to provide unobstructed access, and this is super in

The current issue is because light is line-of-sight. Such systems traditionally need a lanyard of some kind to provide unobstructed access, and this is super inconvenient for the user. Then there's the problem of means-of-detection; Phillips had a cool setup that relied on the rolling shutter of phone cameras; but as soon as someone comes up with a global shutter for phones, such systems are toast.