I gotta button right behind the driver side seat belt and have no idea what it is for!!! I looked In the books and online and can't find anything. Any ideas??

 

theres a red LED on it, when u lock your car/set the alarm it blinks.

this mean its active
if it dont blink its not active.

what it is, is a button wich turns your interior alarm sensors on/off.

its used for(ideally) if you have kids or pets in your car or if your windows are left open to prvent the alarm form going off, when you lcok your car/set alarm.

if you close your windows and dont lock moving things(i.e. kids or pets) in your car, then keep it on for safety safe, of your vehicle that is

 

Alarm motion sensor disarm button.