Alarm going off after a few hours

I have an 02 Rover 75 and just yesterday this issue occurred at night. The car has been parked and locked by fob outside the house for several hours when the alarm starts going off. We go outside to see whats what but nothing wrong,no doors open or windows or bonnets or anything. So lock it again by fob and after an hour it starts going off once more. We leave it unlocked this time for a few hours and all is ok, start it up for a few minutes and then lock it by fob once more. All is ok until 4am this morning when the alarm starts going off once more so it has been left unlocked since.

Anybody any ideas what is causing this?

Also just wondering if there was a way to disable the alarm completely? As long as the doors lock Id be happy to do without an alarm.

from the last news http://ift.tt/1Ej19Z7

via IFTTT