Remote Buttons

OK I opened up my remote today to change out the batteries and low and behold I discovered that in fact there are two buttons on that badboy. You can see what I assume is the second button, recessed into the face of the unit under the first. SO I immediately went out to the car and started pushing the button, nothing happens. Of course now I wont be able to sleep trying to figure out what it is supposed to do. Or maybe its not a button at all. Help please.

0260N4