Wednesday, December 2, 2009

Usability: Locking Doors

Reading The Design of Everyday Things has caused me to start paying attention to usability issues I run into in day to day life. Some of them are interesting and I'm going to try to remember to share those here.

This one is about doors. DOET talks a lot about doors. The specific part I want to talk about is how they lock. A normal door works something like this:
  • Use the lock mechanism to lock the door
  • When locked the door cannot be opened
  • Use the lock mechanism to unlock the door
  • When unlocked the door can be opened
A while back I encountered a door that worked differently than this though. Unlike the normal door, which when locked can not be opened, this door could still be opened from the inside even when it was locked without unlocking it! But it could not be opened from the outside when it was locked.

You can see where the designers were coming from here. The point of locking the door isn't to keep people inside locked in. The point is to keep people outside from getting in. Letting you open the door from inside even when it's locked aligns more closely with the purpose of locking the door. And you can imagine all kinds of situations where this would be nice: answering the door when someone knocks, opening the door to leave the house, etc.

So this change seems to be a great idea: it fits the purpose more closely, and it eliminates some small annoyances. Unfortunately it introduces a really big annoyance of its own: its super easy to lock yourself out.

All you have to do to lock yourself out of the house is walk out and close the door behind you.

Preventing you from locking yourself out of the house isn't one of the stated purposes of a normal door, but because of how it works it manages it all the same.

But lets look at how a person uses the door the way a software engineer looks at a person using software, in terms of "clicks". Lets assume the door is already locked and a person wants to leave the house and leave the door locked behind them.

With a normal door:
  1. Unlock the door
  2. Open the door
  3. Close the door behind you
  4. Lock the door
With the special open-while-locked door:
  1. Open the door
  2. Close the door behind you
Which of these doors is better designed?

1 comment:

  1. I think which door is better designed depends on what the purpose of the door is, much like the design of your software is dependent on the purpose of the software. If the purpose of the door is providing a secure access point to a location, then the door which allows you to leave the location without unlocking the door is probably better designed, because you don't have to worry about the user having to lock the door after exiting the location.

    If the purpose of the door is to provide an access point with optional security, then the door you have to actively lock and unlock has the better design because you have the option for security. I think a better design would be one such as newer car doors. If locked, you can't open them from the outisde. If you're inside, you can open the door and the door becomes unlocked. So, you've got to actively lock the door once the door is opened.

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