Actually, security through obscurity is the only option on a car. No alarm will keep a thief out and you can't fight back legally, so the only thing left is to have a dull-looking car. (and maybe a bear trap inside the dash as backup)

My Cherokee Sport had it's Alpine stolen a few years back, but that's just because my stupid housemate kept leaving the garage open and I didn't lock the Jeep when it was in the garage. User error on both counts.

-Hoagy.