Key button
 

Purchased an '02 BS couple months ago. Key I have has a small button on the side of it that I can't find any documentation on. Any clue on what it does?

My 2002 base has a tiny button activated flashlight on the valet key. Could this be what your are referring to?

Are you talking about the central lock/unlock button near the radio?

You're talking about the little square button on the side of the key? You would press that to actually open up the key and access the battery.

I have a 2001 Boxster base with no remote key but strictly a manual key with a button which if pressed should light up a small bulb in the key which helps you find the keyhole. I pried it apart after taking the key off the key ring. Inside mechanism is really delicate which operates the light. Got a new battery and replaced the old one.
Worked a few times then the internals broke. If I remember right I pried open the cover of the key with a penknife.

The tiny little "button" on the side of the remote key is the pin (on a spring) that holds the keyblade into the remote. If you take the button cap off, it'll be easier to see. :)