This Power Supply is suitable for the Modular Burglar Alarm. However, it has other applications. It is designed to provide an output of 12-volts, with a current of up to 1-amp. In the event of mains failure, the back-up battery takes over automatically. When the mains is restored, the battery recharges. Use a genuine alarm type back-up battery. They are maintenance-free, and their terminals can be held at 13v8 for many years, with no ill effects. A smaller or larger capacity battery may be used, without circuit modification.