Sorry for digging up this old thread.
I have exactly this problem with my 06 Grand Voyager. And it only started since i welded a patch on the sill, beneath the nearside sliding door. Yes, i had disconnected the battery before doing so. Yes, i made sure no part of the wiring loom was close enough to my welding to get damaged. Now the alarm goes off randomly, often in the middle of the night, but usually soon after the car has been locked, armed and left. In desperation, i sought out the VTSS siren and unplugged and removed it. (I can confirm it is behind the bumper, below the nearside headlight, as shown in the pic upthread). If the siren has an internal battery, that might have been damaged when i was welding, BUT, the alarm is still going off randomly (the telltale light below the instruments is still flashing quickly after the car has been locked/armed with the key fob), it just doesn't now have a siren to make any noise with. I will be continuing to try to figure this out as for the previous five years we've owned this Voyager, the alarm has been faultless.
