Possibly a problem with the ultrasonic, also worth checking that there wasn't an alarm component on the same fuse as ther EAS.
Odly, my sister's had an after market alram fitted inplace of the original and when that one imobilises, whether you locked the doors or it just does it on the 30 second timer (Thatcham cat 2) then the EAS self-levels which normally means it drops an inch or so :-k
Anyway, perhaps more likely, there is a connection to the EAS from the door pin switches to dissable the EAS when a door is open (so it won't drop onto a kerb),perhaps this wire is also shorting to earth like the power supply wire was before.
If you replace the C/L fuse then lock by the key, the ultrasonics are not activated (pet mode), if it still goes off then trace the door switch wire to the EAS ECY plug.
