The control panel battery is I likely cause of your problem.
Unfortunately you can't test it without the correct test equipment,so I'd say replace the battery.
Also it would of been nice to know the model of the alarm in question,also what keypad led's are lit and if lcd,what it says.
So mains off first before you open the panel,then replace the battery like for like observing correct polarity.
Good luck and be safe :)
e manno, July 2013