Best way to describe this would be if your take your finger and press right below the volume/mute knob, it feels like another button.
This is probably useless without pics, so I can take one when I get home. Just a random observation, when I was putting the unit up before heading out. Doesn't move by much but you can most certainly feel it when you press on it, not hard, just a regular key press type of push.
And, no I'm not trying to up my post count