Sorry for the newbie question, but I can't find anything in the owner's manual, and my service disk hasn't arrived yet. I have two sensor looking things in the center of the dash, just under the windshield -- one lights up to indicate that the alarm is engaged, but what is the other one? The reason I ask, is that the plastic piece over the defrost vents (which incorporates the sensors) is horribly cracked. I picked up a used on on e-bay, but it only has a hole for incorporating the alarm light, not the other sensor...