With rumors of so-called smart watches coming to market, U.S. researchers say they're trying to figure a way to type on the tiny screens of such devices.

With Apple, Google, Samsung and Microsoft rumored to be developing such devices, engineers are pondered just how people will enter an address, a name, or a search term into the small screen of such ultra-small computers.

Researchers at Carnegie Mellon University say they've developed and tested an "iterative zooming" technique that may be an answer.

Dubbed ZoomBoard, the technique is based on the familiar QWERTY keyboard layout. Although the full QWERTY keyboard is impossibly small on a watch-size display, tapping the screen once or twice will enlarge an individual key until it can be comfortably and accurately pressed, the Carnegie researchers said in a release Tuesday.

Capital letters can be typed with a long press on a key; a swipe to the left deletes a character while swipe to the right types a space, and an upward swipe calls up a secondary keyboard of numbers and other symbols.

"You aren't going to write a novel, but it gets the job done," doctoral student Stephen Oney in Carnegie's Human-Computer Interaction Institute said. "This opens up new possibilities for devices such as smart watches, which generally lack any means of entering text, as many aren't powerful enough for voice recognition."

The researchers said they opted to use the traditional QWERTY keyboard layout because the configuration is instantly familiar to users.

"Users can enter about 10 words per minute at high accuracy on a keyboard the size of a penny," researcher Chris Harrison said. "That's plenty fast enough to dial a phone number, or enter 'where is pizza?' or get 'directions home.'"