The Battery
The most common cause of problems with Security Alarm Systems is the Back-up Battery. This battery is a lead-acid battery just like the one in your car except instead of liquid inside it has gel. It has a life expectancy of 3 to 5 years but may last longer than that.
The best thing to do is to have it checked annually along with a full check of the whole system.
If your keypad starts beeping or your alarm starts playing up, most likely it will be the battery. Get a security technician to change it for you.