I'd think the most likely cause of your inop factory alarm is an aftermarket performance chip. I understand many guys will have them burned w/o the alarm feature thus disabling it ...
I'm pretty darn sure the factory alarm does not go thru the chip... believe is is just a starter circuit disable via a relay.... never heard of an 'alarm' option on a chip burn... I could verify this, but I'm lazy... :wink: and I think the OP has verified via the RPO that the car is not equipped with the alarm anyway, just stickers on the windows, which to my knowledge, weren't put there by the factory.... someone correct me if I'm wrong...