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I may be mistaken but I think they're the internal security sensors. They'll set your truck alarm off if, say, you leave a kid in the truck and they move around.
Yes, I had that happen once. Was borrowing my FIL's '22, he wanted to stay in the truck so I locked it (I could see the truck through the window of the building) but I didn't set the alarm to perimeter only...he switched seats in the back seat and the alarm started going off.