What Happens to Your House Alarm During a Power Cut?

Power cuts are a fact of life in Ireland — especially during winter storms. If you have an intruder alarm, you might wonder: will it still work when the electricity goes out?

The short answer is yes — every professionally installed alarm has a backup battery. But there’s more you should know.

How Alarm Backup Batteries Work

Your alarm panel runs on mains power (240V) but contains a rechargeable backup battery that kicks in automatically when the power goes out. The system continues to operate normally — sensors, keypads, sirens, and (if fitted) the communicator all keep working.

When power returns, the battery recharges automatically. Under EN 50131 Grade 2, the battery must support the system for at least 12 hours.

How Long Does the Backup Battery Last?

Panel battery (12V rechargeable):

• Lifespan: 3–5 years
• Standby duration: 12–24 hours depending on system size and activity
• Recharge time: 24–48 hours after power returns

Wireless sensor batteries:

• Lifespan: 2–4 years
• These are separate from the panel battery and continue working during power cuts

If your battery is older than 5 years, it may not hold a full charge. We check and replace batteries during annual maintenance visits.

What to Expect During a Power Cut

Normal behaviour:

• The alarm continues to work silently
• Keypads may show a “mains absent” or power icon
• Sirens won’t activate unless an intrusion is detected
• Monitored systems continue sending signals (via GSM/radio if the communicator has backup)

If the power cut lasts a long time:

• The keypad may beep intermittently to warn of low battery
• If the battery runs flat, the system shuts down — but the external siren may still trigger (it has its own battery)

After the Power Returns

Check your keypad for any fault messages. Common post-power-cut issues:

Fault Message	Meaning	Action
”Mains Absent” or power icon	Battery didn’t recharge yet	Wait 24 hours; if still showing, call us
”Low Battery”	Panel battery needs replacement	Schedule a service visit
”System Fault” / “Engineer Required”	Battery or component fault	Call us on 091-771010
”Fail to Communicate”	Broadband/phone line down	Check router; if persistent, call us

Why Your Alarm Might Beep After a Power Cut

Intermittent beeping from the keypad usually means:

• Low battery — the battery was depleted and needs replacement
• System fault — a component didn’t restart correctly
• Clock reset — the panel’s internal clock may need resetting (we do this during service)

Entering your user code usually silences the beep temporarily, but the underlying fault needs fixing.

How to Prevent Power-Cut Problems

1. Annual maintenance: We test the battery, check charging circuits, and replace batteries before they fail
2. Upgrade old batteries: If your battery is 5+ years old, replace it proactively
3. Consider a monitored system: GSM/radio communicators (like CSL DualCom) have their own backup and don’t rely on broadband or phone lines
4. Tell us about planned power cuts: If ESB Networks notifies you of maintenance, we can put your system in a special mode

The Copper Phone Line Switch-Off

With Eir withdrawing copper landlines, many older alarms that relied on phone-line dialling no longer work during power cuts (or at all). Modern systems use IP or GSM communicators that are unaffected by the copper switch-off.

If your alarm is more than 10 years old, it may need upgrading. We can assess your system and recommend the most cost-effective upgrade path.

Maintenance Contract Benefits

Our maintenance contract customers get:

• Annual battery testing and replacement before failure
• 24/7 emergency call-out with a 3-hour response guarantee
• Priority over non-contract customers
• Discounted parts and labour

Need Help?

If your alarm is showing a fault after a power cut, call us on 091-771010. We can often diagnose the issue over the phone, and our maintenance customers get free telephone support.

Not on a maintenance contract? Learn about our maintenance plans or request a quote for an upgrade.

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Centaur Alarms is PSA licensed (No. 96) and has been maintaining intruder alarms in Galway since 1996. All our systems are installed to I.S. EN 50131-1 with documented battery compliance.

Tags: power cut, backup battery, alarm fault, maintenance, troubleshooting