COIN, a monthly indicator of current activity.

ECONOMIST: Overview

The tiny current produced is harmless in itself, but the flow of charge drags nickel ions out of the coin and on to the skin.

ECONOMIST: Why the euro may be a rash move

Droplet is a compact self-contained module with an integrated RGB LED, a photodiode and a CR1216 lithium coin battery -- which provides roughly one day of power in the gadget's current early prototype status.

ENGADGET: Droplet and StackAR bring physical interface to virtual experiences, communicate through light (hands-on)