Well as you know I had similar problems last week.
I also ruled out the battery and ensured that everything connected to the alarm where closed (glove box, doors, windows, trunk, gas cap, hood, basically everything that opens or closes). Car is parked in a level garage and since that first night where it went off a couple times I have not had any problems since ... knock on wood. Wish I could help with a solution but I guess it is just all about chasing the ghost till you find something that works. Good luck, and apologize to your neighbors in advance.