Came across this post a few times while dealing with a random alarm the last few months(multiple times a day). A few notes in case someone is reading this from the same situation I was:
1.If you use the actual key blade (take it out of the fob, put it in the driver door, and turn) it will lock but not arm the alarm system.
2 .Buy a scanner. (I think I searched “gm tech 2” on Amazon.) I bought one specifically listed for “gm” for about $150. Or get it scanned at a dealership, which might cost more than a scanner, but it’s simpler if you’re not tech inclined. On scanner, under BCM there is a “content theft alarm” that lists the alarm trigger history(my scanner shows the last three). Mine listed “hood” and that is where the problem was. Latch was sitting too low and was switching the sensor from open to close at random. Hope this helps someone. Get it scanned, don’t waste your time on a wild goose chase.