When an alarm sounds after power restoration and the code is lost, start by locating the control panel. Wait a few minutes, then reconnect power and battery. This guide provides simple, step-by-step instructions to restore your system to normal operation and clear the fault indicators that remain after power has been re-established. The security system is designed. PRATICAL POWER BACK ALARM: This utility power return alarm is mainly used during a power outage, its voltage sensing antennae can detect the voltage change. Recommendations happily considered. When the mains power is cut, the main control panel's battery cannot sustain the system, causing the external sounder to activate and alert you to an issue.