Short answer
The panel switches to its backup battery and keeps protecting the house, usually for several hours to a day depending on the battery and how many devices it powers. It can still call for help if its communicator has power and a working path. Cellular radios usually do, but internet-based communicators fail when the router loses power. Expect an AC-loss trouble beep, and possibly a low-battery warning that clears a few hours after power comes back.
On this page
During the outage
- Protection continues. Doors, windows, motion, and system smoke detectors keep working on battery power.
- The keypad beeps and shows AC LOSS, NO AC, or a trouble light. Silence it with your code. See keypad beeping.
- Keypad backlights may dim or turn off to save power.
- Battery runtime depends on the battery size and the load. A typical wired panel with a 7 Ah battery runs for many hours; panels powering lots of wired motion detectors, keypads, and modules run for less.
Can it still reach the monitoring company?
| Communication path | During a power outage |
|---|---|
| Cellular radio in the panel | Usually works, powered by the panel battery |
| Internet / Wi-Fi | Fails when the router and modem lose power, unless they are on a UPS |
| Traditional copper landline | Usually works (the phone company powers the line) |
| VoIP, fiber, or cable phone | Fails when the home equipment loses power, unless it has its own battery |
App-based systems with cellular backup (for example Ring Alarm with its Pro plan) keep reporting through cellular when Wi-Fi goes down. Without that plan, they keep sounding locally but may not notify anyone.
When the power comes back
- The AC trouble clears on its own, sometimes after a short delay.
- Honeywell VISTA keypads may show dI for about a minute after a full power-up while the panel initializes. That is normal.
- A low-battery warning can linger while the battery recharges. Give it up to a day.
- If the panel went completely dead, it may have lost its clock (DSC trouble 8). See DSC trouble codes.
If the panel died during the outage
A panel that shut down before the power came back has a weak battery. Replace it before the next outage: see replacing the panel backup battery. A battery that is three or more years old is due anyway.