Ok...battery was flat,just about opened the doors,alarm went off for a few mins at a time with indicators very dim,car dead,wouldn't start.
Disconnected the battery to charge but alarm went off again...is there a back up battery?
Started her with jump leads and let it run a while...opens and closes and starts ok and was able to disconnect the battery without the alarm going off so guessing there wasn't enough power to deactivate the alarm....so I'm sorted but is there anything to do when the alarm goes off when the battery is low and disconnected?
I believe the actual siren unit itself makes a noise when its disconnected/power drains - shouldn't go off for long though as it quickly powers down, if its the normal alarm you should be able to disable the alarm with the fob etc as there should be enough power for that.
I have found that if the battery is dead:
Unlock the car manually
Open the engine lid
Close the driver door
Unplug the lid sensor on the top left
Attach the jump pack
Unlock the car as you would do normally to deactivate the alarm - the car doesn't know the engine lid is open as the sensor is disconnected