if its in working condition which it sounds like it is keep it pal just change that battery inside the box when you do that the alarm will sound but its nothing to worry about just key in your code when it does that followed by reset and when the cover is refitted it will automatically go back to day mode
my first question is was the front door or the door to leave your house open when zone 1 was illuminated
second question; I would set the alarm off to see if the outside box is working because the connector blocks on these old sounder/strobe box's rust and eventually stop the alarm working
Nick
February 2015