Eventually, wearable displays might be so thin that they effectively blend into your skin. University of Tokyo researchers have developed an optoelectronic skin whose polymer LEDs and organic photodetectors are so thin (3 micrometers) that they practically blend in with your body. If it weren't for the thin film needed to attach the display in the first place, it'd look like a tattoo. The technology more efficient than previous attempts at these skins, running several days at a time, and it's durable enough that it won't break as you flex your limbs.
As you might have gathered, the current hardware is a bit crude. The prototype you see above doesn't do more than tell you your blood oxygen concentration levels. However, the scientists are dreaming big. They see a day where runners could have fitness data on their hands, or workers could put diagrams on their wrists. In that sense, smartwatches could just be stepping stones toward truly seamless wearable tech.