8.5. Shake, Shake, Shake

When the iPhone first debuted, its built-in motion detector (the accelerometer) was a delightful novelty, and it inspired a corresponding number of first-generation novelty apps. Your iPhone could be a light saber, a glass of beer, or a shotgun. Give it a tilt, a shake, a wiggle, and your iPhone responded with animations, sound effects, you name it. The shiny new hardware feature proved irresistible to developers of more staid apps, too, who experimented with using hand waving gestures to trigger some actions—moving the iPhone itself as an alternative to touching the screen. In particular, the shake gesture showed up everywhere and for all kinds of uses: Urbanspoon used shake to choose a random restaurant; Facebook used shake to load new content; PCalc used shake to clear the current calculation; and Etch-a-Sketch used shake to erase a drawing.

Even at the time, here's what all of those developers knew: shake is a gimmick, a cute novelty more than a useful gesture. While shake works well for casual entertainment apps—it's great for games and music apps—or to support an interface metaphor like triggering Urbanspoon's slot machine, it's a disruptive and awkward motion for other uses. Shaking draws attention unnecessarily to the hardware and away from the task at hand. When you're tapping away and focused on the screen, shaking the entire device pulls you out of your flow and, afterward, forces you to find your place again onscreen. It's not exactly the most discreet gesture, either: it's tough to keep a low profile in a public place or a board meeting when you're waving your phone vigorously to get something done. While shake is awkward to perform on demand, it's also all too easy to trigger by accident. A quick jog, a speed bump, or an over-caffeinated morning can all yield unintended shake gestures. That means that it's an especially bad idea to use shake for a destructive action like deleting content or clearing a screen.