Many homeowners install alarm systems to ensure that their home is protected from intruders at all times. But if your home experiences a power outage, the lack of AC power could leave your home temporarily unprotected. To avoid this problem, modern home alarm systems often include a backup battery function to prevent the electricity to your system from being disrupted during power outages. However, even with a backup battery, some alarm systems may display an error message after the AC power comes back on. You'll have to reset the system to clear the error message.
Locate the "System" or "System Status" button on your home alarm keypad. Press the button twice, in quick succession, to silence the "No AC Power" alarm.
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Wait until the AC power is restored to your home. Take the system's backup battery out of the alarm keypad.
Lift the cover of the circuit breaker box and find the breaker that controls your home alarm system. Move the breaker into the fully "Off" position; flip the breaker back to the "On" position after five minutes have passed.
Replace the backup battery in the home alarm keypad. Install a brand new battery, if desired; note that most home alarm manufacturers recommend replacing the backup battery every 12 to 15 months. Install a new battery any time you get a low-battery message on the alarm control panel.
Enter your user code into the home alarm keypad; press the "Off" button. Re-enter your user code and press the "Off" button a second time to reset the alarm system.