2004 Volvo Alarm going off



My Volvo XC70 was sitting in front of my house very early Sunday morning and the alarm went off, for the 1st time ever. I reset it with the key fob after making sure nobody had tried to break in and it went off again an hour or so later. I reset it again and it went off again after about an hour. Then I left it unlocked. I locked it one more time during the day and it went off. Anybody have any experience with these things. I hate to go to the dealer without any idea what is going on with the car.