Our security system is beeping and we can not turn it off. I have checked all windows. We can not find manual or instructions and cannot remember our code.?? How do we turn off the system and not activate the main system. Maybe the back up battery is bad?It is at least 3 yrs old. How do we remove it? The code on the box is: VistaADEMCO VISTA-20P -20PS1A -15P -15PS1A battery 1240 12V4AH/20 hr