There is a small, rectangular, plastic-looking, button?/panel?/thing? on the underside of the trunk bar, just to the right of the license plate lamps.

What the heck is that ?

 

Since you neglected to mention, or add it into yoru profile, I'm going to assume you have a 2004+.

That is button to unlock your trunk while the smart key is in proximity.

 

My '01 UL has a 1"x2" or so spot on the right hand side of the underside of the trunklid.. looks like there should be a switch or something there, but there is just a black plastic plug. Reminds me of the hatch release on an RX..

 

Sorry - I have an early 2004 (w/o SmartKey), so I guess it's a plastic blank on mine. Thanks for the info.