medic

I am currently borrowing my sisters '05 or '06 trailblazer for a few months (don't know what year it is). MY problem is that the alarm system keeps re-alarming itself even when the dorrs are unlocked after 30 seconds. I asked her how to turn it off, but she didn't know. Under the dash there are 2 switches, one for the automatic start and the other is a black button that does nothing when I press it. She thought that was for the alarm but I don't know. Anyone know how to disengage it so I don't have the alarm going off when I open the door? Thanks