Apple (News - Alert) was recently granted a patent for a ring device that the user would wear on the forefinger, while the adjacent thumb would be used to manipulate its screen. It would come with several sensors that measure various biometric conditions and be able to digitally record handwritten notes.

According to the patent application filed with the U.S. Patent and Trademark Office (USPTO), the ring device would contain its own computer processor and be configured to communicate with an external device, such as a smartphone. It would also have a microphone capable of responding to commands from the user and be capable of recording video or taking still pictures.

A term that appears frequently in the patent application is haptic feedback or haptic. This typically refers to user interface features that use the sense of touch to communicate that a control of some kind was pressed. Smartphone users get haptic feedback for example, when the user presses on the device’s touchscreen and it vibrates in response.

It would be almost impossible to use a device as small as a ring without at least some haptic feedback, since an array of mechanical keys and buttons would be impractical. In the case of Apple’s proposed ring device, haptic feedback is given to acknowledge commands, either verbal or from touching a screen or to give directional feedback through the use of primary and secondary actuators.

One of the obstacles to a ring device being successful in the consumer marketplace is ring size. According to the Jewelry Making Journal, there are 17 standard ring sizes in the U.S. alone, which excludes more precise half and quarter sizes. Managing the inventory for all these different sizes could be tricky, and if the device sold a lot of units, custom measuring and ordering would become unwieldy.

It remains to be seen whether or not a ring device is something the consumer market has great interest in. Perhaps the most significant conclusion you can make about one is that there seems to be no limit as to how small a functional wearable device can be.