My burglar alarm keypad is locked and displaying 11. It is now non responsive when I try to type in a code. We had a power cut for an extended period and I suspect the back-up battery is run down. It has not been changed for about 10 years. The trouble is I am frightened to change it because not being able to get the keypad to respond I will not be able to cancel the alarm when the tamper activates it. Any ideas or suggestions? Thanks1