Researchers at the MIT Media Laboratory are developing a new wearable device that turns the user’s thumbnail into a miniature wireless track pad (for controlling the position of a cursor on a screen, for example).

They envision that the technology could let users control wireless devices when their hands are full — answering the phone while cooking, for instance.

It could also augment other interfaces, allowing someone texting on a cellphone, say, to toggle between symbol sets without interrupting his or her typing.

And it could enable subtle communication in circumstances that require it, such as sending a quick text to a child while attending an important meeting.

The researchers describe a prototype of the device, called NailO, in a paper they’re presenting at the Association for Computing Machinery’s Computer-Human Interaction conference in Seoul, South Korea.

According to Cindy Hsin-Liu Kao, an MIT graduate student in media arts and sciences and one of the new paper’s lead authors, the device was inspired by the colorful stickers that some women apply to their nails. “It’s a cosmetic product, popular in Asian countries,” says Kao, who is Taiwanese.

The researchers envision that a commercial version of their device would have a detachable membrane on its surface, so that users could coordinate surface patterns with their outfits. T

They used capacitive sensing — the same kind of sensing the iPhone’s touch screen relies on — to register touch, since it can tolerate a thin, nonactive layer between the user’s finger and the underlying sensors.

Instant access

As the site for a wearable input device, however, the thumbnail has other advantages: It’s a hard surface with no nerve endings, so a device affixed to it wouldn’t impair movement or cause discomfort.

And it’s easily accessed by the other fingers — even when the user is holding something in his or her hand.

To build their prototype, the researchers needed to find a way to pack capacitive sensors, a battery, and three separate chips — a microcontroller, a Bluetooth radio chip, and a capacitive-sensing chip — into a space no larger than a thumbnail.

For their initial prototype, the researchers built their sensors by printing copper electrodes on sheets of flexible polyester, which allowed them to experiment with a range of different electrode layouts. But in ongoing experiments, they’re using off-the-shelf sheets of electrodes like those found in some track pads.

They’ve also been in discussion with battery manufacturers — traveling to China to meet with several of them — and have identified a technology that they think could yield a battery that fits in the space of a thumbnail, but is only half a millimeter thick. A special-purpose chip that combines the functions of the microcontroller, radio, and capacitive sensor would further save space.

At such small scales, however, energy efficiency is at a premium, so the device would have to be deactivated when not actually in use. The researchers found that requiring surface contact with the operator’s finger for just two or three seconds was enough to guard against inadvertent activation and deactivation.

“Is it the case that we’ll all be walking around with digital fingernails in five years’ time?” Hodges asks. “Maybe it is. Most likely, we’ll have a little ecosystem of these input devices. Some will be audio based, which is completely hands free. But there are a lot of cases where that’s not going to be appropriate. NailO is interesting because it’s thinking about much more subtle interactions, where gestures or speech input are socially awkward.”

Melanie Gonick/MIT | NailO: A thumbnail-mounted wireless trackpad

Designed in the MIT Media Lab, NailO is a thumbnail-mounted wireless track pad that controls digital devices. Watch it in action.