Each Wall-E unit has an integrated audio recorder with three buttons: Record, Play, and a third button with an orange square. We see Record and Play used several times, but the orange button is never visibly pressed. Reason and precedent suggest it is a stop function.
What the original purpose of this capability is unclear. Wall-E uses it to record snippets of songs or audio clips from movie that he enjoys. There is no maximum length shown. There is no visible method to rewind, fast forward, or seek along the soundbite, though the clips shown are short enough that it doesn’t affect Wall-E’s ability to hear what he wants to hear.
This is a very simple interface, and Wall-E is shown being able to operate it without looking at the buttons. Since all three are relatively large, placed on the front of his chest, have physical indentions, and are physically separated, it would be possible for a person with a tactile sense to tell the buttons apart once they learned the order of buttons.
Increasing the indentation of the symbols, and adding a different texture on each would make tactile discovery even easier.
The recording capabilities shown are also short. This means that it is excellent for a contained thought, song, or event to be referenced later. Short clips allow the user of the system (in this case Wall-E) to never need to worry about where the recording is cued up to, and play whatever it is he remembers being in memory.
The Orange Button?
Unlike the Play and Record buttons, which are shown meeting standard interface practices of today, the lineup has that odd orange button that is never shown being used (except when Eve is frantically trying to wake Wall-E up, but that tells us nothing about its intended use).
My best guess, based only on its inclusion with the other two buttons, is that it represents a pause function or stop. This conjecture isn’t 100% certain because either function could easily be co-located on the play button as a dual function. Push once to play, push a second time to pause.
So what is the orange button for?
The lesson here is that when you’re designing an interface, make sure that each button is absolutely necessary and well placed. Given the location and tactile focus of the interface, the two most used functions (record and play) should have been larger and had distinguishable texture. The third button has a less-than-obvious purpose, meaning that any humans attempting to use it in the far future will need to use trial and error to understand what it’s for.
Two of the buttons are easy to understand. But designers for this system would want to make sure that a person with no access to documentation could quickly understand the third button through immediate feedback and a function that is non-destructive to the data stored in the audio recording.