Firex Smoke Alarm problem please ... Hi, I have Firex smoke alarms throughout my home one of which is bleeping every minute which I understand is an indication that the backup battery need replacing. I'm not sure which model they are as there is no number on the units however, the design indicates: 1240C, GC240 or IAR230C. The cover says to unscrew turning anti-clockwise but it just wont turn and appears to be splitting at its centre base unit attached to the ceiling. Can anyone help/advise please?