Sunday, March 14, 2010

Problems On and Off

Some time ago my sister called with an urgent question. "The battery on my new iPod keeps running out. I have to leave it plugged in all the time."

"So turn it off when you're not using it."

"I don't know how to do that. There's no OFF button."


I hadn't an iPod, but I did have an iPod Shuffle. The Shuffle had a simple slider switch with three positions: off, on, and shuffle. On played recordings sequentially, shuffle arbitrarily. The volume control on the earpiece cable had clear labels: + (louder) and - (quieter). Anyone could understand the device's operation after experimenting less than 5 minutes.

I had no clue how to turn off her iPod.

I asked my son who also had an iPod Classic. "Oh yeah, hold down the play button until it turns off."


Keeping in theme, let me offer that my sister is not broken.  She's a Ph.D. psychologist (Fuller Seminary), holds a license to practice in California, and, at the time of her query, ministered to the mentally ill in California's maximum security prisons. She had purchased the unit to listen to recordings needed to fulfill her continuing education requirement. She could not turn off the unit because it has no OFF button.

The Real Problem

As do many devices, the iPod Classic switches on whenever the user presses any control button. It switches off only when the user presses and holds a specific button. Its design violates the natural mapping of a symmetric operation, ON/OFF.

Consider most houses' lighting switches. Switch placement is usually handy to a room's entrance. ON/OFF is simple and clear: a single movement and its reverse control the light. The action is symmetric and compact.

Now imagine a room in which any action — turning the door handle, touching a wall panel, opening a door, clapping — turns on the lights, but to turn them off residents must find, touch, and hold a small panel labelled light. What would happen?

That's right: the lights in the room would burn forever. Lamps and other devices, just like my sister's iPod, would remain on, constantly chewing power. No one would bother to turn them off because it was too much trouble to find the light switch.

There is no energy crisis. There is an OFF button crisis.

Today it's so easy to turn stuff on, so easy in fact that now many things turn themselves on. What people cannot figure out is how to turn stuff off. People have given up in frustration. They no longer care that stuff is still on and they just leave the room.

Fixing the Design

ON/OFF is a critical function. When something goes wrong, it's the "kill" switch, the switch of last resort. For example, automotive "unintended acceleration" incidents would halt (or happen less often) if drivers had the presence of mind to switch the ignition off. The engine would die and any mis-application of the throttle pedal would cease to speed the car. OFF saves lives.

Good ON/OFF control design must
  • make the control distinct (keep it apart from other functions);
  • make the control compact (locate it in a one spot);
  • ensure the control is prominent (put it where it's easy to find); and,
  • be clearly labelled (unmistakably identify it).
Will these rules ruin "smooth" industrial design? Perhaps. But the customers will be able to turn off their machines and the world will be a quieter place.


Special note: Happy Pi day!