Alarm keeps going off while parked??

[tzincp]

When parked and locked my car's (986) alarm will randomly go off, sometimes within an hour, sometimes hours later or the next morning.

I have been scratching my head with this for some time. When I lock the car it acts normally- gives two beeps a second or so later.
I have gone through and made sure both doors, trunks and the center console are closed and it still happens.

I'd rather not just unplug the alarm horn, any ideas how I could trace the issue? My durametric doesn't seem to show what sensor is tripping this.:ah:

Thanks for the help