Factory alarm went off today for unknown reason

[CGALATE]

I was at work, truck was sitting in my driveway. Got home everything was how i left it, closed doors and locked it. The security light on dash will not flash. Anyone have thoughts about this situation?
2003 laramie 4wd auto

 

[bighammer]

Mine did that a long time ago, (early morning, small village) and wouldn't shut off. I ended up unplugging the horns. I couldn't figure out what set it off and didn't want a repeat, so I wired the steering wheel horn button to a relay to control the horns. Sometimes the alarm would go off, (like opening a locked door thru window) and the lights would just flash; it became a silent alarm.

 

[p-Bar]

Mine does it every once and awhile. I just reset it.

 

[Ozymandias]

Mine to, i got used to always double push the "open" button on the FOB as sometimes it seems to open but doesn't disarm the alarm system on the first push.