>>I've been away for 4 months <<
Have you had some type of trickle charger (such as the solar panel) on the battery during this time?? I believe that the alarm "goes to sleep" after a period of time to conserve the battery, but...
I would disconnect the battery for a while, charge it up, and see how the car behaves (you may need to re-program the radio... so make sure you've got your code!!)
Yuri.