Hacking Lumi Deco Nails

On my last trip to Tokyo, I picked up a set of tiny nail stickers called Lumi Deco Nails, released by a Japanese toy company called Takara Tomy Arts in April of 2014. They’re touted as the world’s first nail stickers with embedded LEDs that glow near NFC enabled mobile devices.  Best part – no batteries required.  The set includes one LED sticker, 16 non-LED stickers and a nail file. It cost me ¥1250 ($12), but sells for $24 in the US.

Being a tinkerer, I wanted to know exactly how it works. Unfortunately, I didn’t find much explanation online other than what I already knew – it reacts to NFC signals and lights up.

I don’t have an Android phone, but true to the manufacturer’s claim the stickers do work with my standalone NFC reader. The closer to the NFC reader I hold the LED sticker, the brighter the sticker gets.  I found that the stickers work better when I hold them parallel to the NFC reader. That instantly felt familiar.  It’s just like how inductive charging copper coils work.

High school physics review: a coil of copper wire generates a current when it’s exposed to an alternating magnetic field.

In this case the NFC signal act as a magnetic field. To quickly test my theory, I made a coil out of silicone wire and attached a small LED to the ends. I placed the coil over the NFC reader and, voila! It lit up just like the Lumi Deco sticker.

I was then able to get a thin enameled copper wire to react the same way (after I stripped off the enamel coating with the nail file that came with the Lumi Deco Nails kit). I made a smaller coil this time, and the LED lit up really bright.

My homebrewed version is still not as small as the Lumi Deco sticker, but pretty soon I’ll have something much smaller and wearable on my finger.  Check out the video below for a demo.