Hi, anyone had this problem: blip once with remote to lock car and a short faint alarm sounds as lights double flash to indicate it's locked. Then after a while I notice lights flashing but no alarm. Have tried unlocking and locking again but still does it after a while. I have checked that all windows are shut. This has only happened recently. It is a 2007 1.9tdi Roomster. Does the siren have a back up battery and its failing?

any thoughts or advice would be appreciated. I have owned the car for 6 years and has been brilliant.

It does have battery backup yes 

 

I suspect that's the issue the battery is mullered