Ok - I had this issue within the first week of having my car back in November 2004, and the dealership had to replace my alarm.

Fast forward to 2011 and my alarm goes off for no apparent reason. The car was sitting in the driveway, alarm set and doors locked, in bright sunshine (it was really hot out), and the alarm just started going off. I reset the alarm and a few minutes later it did it again. It is also going off inside the garage, outside at work, etc.

Anyone have any ideas or suggestions?? This is driving me absolutely nuts!

 

My '06 did this in the garage.
Drove me nuts until I discovered there was a moth trapped inside.

 

That's what I was thinking. Perhaps there's something trapped inside that is setting it off.