This is just my opinion, but Ive never liked factory alarms...I like how mine goes off if someone even bumps into me...Id rather run out to my alarm and see the guy trying to drive off so I can get his tag, rather than coming out the next day with a big red stripe down my car.
Yours probably doesnt have an alarm, thats just the
PATS security light. Which you would probably not want to turn off, because anything that gives the impression of the truck having an alarm is a good thing.