Here are two little behind-the-scenes videos from Terminator Salvation. The first is a little shorter. If you don't like SPOILERS don't watch them, though I'm not sure how much of spoilers it is showing considering the trailers reveal stuff...just watch them.
Behind-the-scenes part 1
Behind-the-scenes part 2
Around the 5:45 mark, listen for the car alarms going off after the mushroon-cloud goodness.