Interesting alarm condition.

Customer bring car in, alarm goes off on its own they say. Check vehicle and experience the alarm goes off after the vehicle is disarmed with the remote and the driver's door opened. We were directed to replace an anti-tilt sensor after some diagnostics were performed.
That did not resolve the issue.
We were then further directed to replace the siren. Not sure why, other than that the batteries go bad.
This did NOT resolve the issue either.
There are NO active failure messages from the NBC.
The last activations indicated the left door. A latch was ordered by the parts department and installed. Of course this changed nothing either.
We have also replaced all the volumetric sensors. Still, NO JOY.
I am personally inclined to believe that there is an NBC issue.
Anyone able to confirm or deny? We use a TEXA scan tool, so not entirely sure if the data given is actually correct.

Thanks in advance.

L