It’s funny to hear people complaining about usability of toys they use. This one is from a friend of mine who just bought a new car a few months ago. The key of a car has two remote buttons:
- one for unlocking a car and
- one for locking a car.
But there are 3 functions associated with these 2 buttons:
- when pressing the unlock button the car opens (which is to be expected)
- when pressing the lock button ONCE the car locks (which is to be expected)
- when pressing the lock button TWICE the car locks and it disables the inner door latches so the car can not be opened from the inside – to prevent someone opening the door from the inside after breaking the window (as it is explained in the manual)
Now the user has two choices: locking the car in a half safe mode (the second option from the list) and locking the car in the full safe mode (the third option from the list) :). The question is why would someone lock the car without this safety feature (pressing the button only once)? My friend is now complaining that he always has to press the button twice to lock the car and he never presses it once because he doesn’t want to leave the car in a half safe mode. 
There is another question to this. Who would like to stay locked in a car and not being able to open it from the inside. Imagine if pressing this button once would lock the door from the inside as well (as my friend would like it to have). Imagine pressing it by accident and being involved in a car crash and not being able to exit. So there’s a user’s safety issue involved. But the same the button could be accidentally pressed twice while being in the car (the possibility for this is small but it still exists) and the driver is in danger again.
This situation has two modes (with the car being locked):
- while in a car I would like to be able to open the doors from the inside (some cars lock the door automatically when the car starts so no
one can for example open the door while a driver is waiting for a green
light at the intersection) - while not in a car I would like not to be able to open the doors from the inside (if that is considered more safe by the automobile industry)
There is another mode in which car is not locked:
- while in a car I would like my doors to be unlocked (some people don’t like being locked in a car for various reasons)
The solution could very simple (with sensors for example). First thing to do is to offload the burden from a user:
- if someone is in a car disable locking the doors from the inside if the lock button is pressed (X times)
- if there’s no one in the car lock it from both sides if the lock button is pressed
Now the user has the same two buttons and the same three functions but locking the car works differently without user knowing it – so concerning the user there are two functions only. Putting it differently there are still two locking modes but the user doesn’t need to know it because it is not affecting her/him directly. User only presses the lock button once.
Edit 22/6/2010: It just crossed my mind; doors could be automatically unlocked in a car accident so someone could open it from the outside to help. It could be done automatically when the airbag fires up for example.
Interfaces that have 3 buttons and 27 features are always considered bad (Donald Norman, The design of everyday things).
