What Happens to Your Security Alarm in a Power Outage?

This guide explains what a security alarm does in a power outage. It is for Melbourne homes and small businesses, and it shows what keeps running, what stops, and what to ask your installer before the next storm. It does not replace the manual for your own system, because every brand and model is different.

Will my alarm work in a power outage?

An alarm is not one device. It is a chain of jobs: sensors notice something, a panel decides what it means, a siren makes noise, and a connection tells your phone or a monitoring company. Each link can have its own power. A blackout may stop one link and leave the others running.

That is why “my alarm is offline” does not mean “my alarm is off”. Your phone app shows whether it can reach the alarm. It does not show whether the sensors and siren still work.

What keeps working in a blackout, and what stops

The diagram shows the usual set-up. Green means it has its own battery. Red means it plugs into the wall and stops unless you add backup. Amber means it only works if there is a path to the alarm. The dotted line is the one way an alarm can still reach your phone while your router is off.

Ajax describes this on its own page about how an Ajax system works in a power outage. The hub switches to its backup battery. Range extenders switch to their built-in battery. Wireless devices keep running on the batteries inside them. Automation and smart home devices that need mains power stop. Other brands work in a similar way, but the times and details differ.

Here is an example. Your alarm connects to the internet only through your router. The power goes out at 6 pm. The sensors and siren keep working, and the panel runs on its battery. But the router is off, so your phone app cannot reach the panel and you get no push alerts. If the panel also has a working mobile SIM, it can still send alerts. This is why the SIM question matters so much.

Ajax lets you choose when it tells you about a power cut. You can get the alert straight away, or only if the power stays off for a set time between 1 minute and 1 hour. A short delay stops a stream of alerts from a flickering supply. Check that the alert reaches you through a path that still works during the outage.

How long will the backup battery last in a blackout?

There is no number that fits every alarm. Brand, model, battery age and how busy the system is all change the answer. Always ask for the figure for your own panel.

For Ajax, the maker’s page gives “up to” times: 16 hours for Hub 2 (2G), 14 hours for Hub 2 (4G) and 15 hours for Hub 2 Plus. Superior hubs list up to 60 hours, depending on the battery. These times assume the hub is disarmed, no detector is triggered and only the mobile channel is in use. In a real home they can be shorter, and a battery loses capacity as it ages.

Ajax also has a Battery Power Saver setting. It can stretch a Hub 2 to up to 70 to 100 hours depending on the model. The cost is that the hub turns off its mobile, Ethernet and Wi-Fi connections until something happens, so your phone cannot see it in the meantime. Ajax also notes that turning it on means the system no longer meets EN 50131 Grade 3. If you need Grade 3, read our guide to Grade 3 security alarms.

Our free Ajax battery life estimator covers the batteries inside Ajax sensors, sirens and keypads. It is a different question from how long the hub lasts in a blackout, so use the maker’s figure for the hub.

What the nbn battery does and does not cover

Many people think the nbn battery keeps the whole internet running. It does not. On a fibre to the premises connection, nbn says its battery back-up gives emergency power to the nbn connection box for up to approximately five hours. Your own router is a separate box that plugs into the wall, so it still goes off unless it has its own backup power.

nbn also says that from June 2024 it no longer supplies a power supply unit with a battery. If you want one, ask your phone and internet provider. Other nbn connection types, such as fibre to the node, are not covered by that battery page. Ask your provider what applies at your address.

nbn does not give advice on specific alarms. Its page on security alarms and the nbn tells you to call your alarm provider and ask whether the alarm will work during a blackout on the nbn. One of its suggested questions is whether your alarm will be able to dial out during a power outage. Ask it exactly as written.

If your question is more basic, such as whether an alarm needs Wi-Fi at all, read can a home alarm work without Wi-Fi or internet. For how the sensors and panel talk to each other, see how wireless alarm systems work.

What to do during an outage

A quick list for the night of the outage

Keep a local way to arm and disarm the alarm that does not need your phone, such as a keypad or a key fob. Make sure everyone in the home knows how to use it. A flat or lost phone should not leave you locked out of your own alarm.

If you see signs of electrical damage, water, overheating or a burning smell, stay clear and get help. That is a job for an electrician, not an app. An alarm technician and an electrician may each be needed to get the system back to normal.

Keep your installer’s phone number and your monitoring account details somewhere other than the alarm app. Agree in advance who will call the company, so the household does not try conflicting fixes.

Check everything after the power returns

Give the equipment time to start up and reconnect. Then check for faults, the armed state and any device that still shows as unavailable. A message saying “service restored” does not prove every part has recovered.

1. Look at the keypad or app for any fault or low battery message.
2. Confirm the alarm is in the state you expect, armed or disarmed.
3. Check that each sensor and the siren show as connected.
4. If you have monitoring, ask the company to run a test signal.
5. Test your phone alerts without setting off a real alarm.

A backup battery that has been drained may need time to recharge. If a fault message stays on, have it assessed. Do not keep cutting the mains power to see whether the battery has improved. nbn gives the same advice for its own battery: it says avoiding turning the main power on and off helps the battery last. If a device stays unavailable after everything else is back, our guide to Ajax devices showing offline helps you tell that fault apart from a blackout.

If the keypad keeps beeping after the power returns, the right fix depends on the brand. Read what the message means before you reset anything. We have fault guides for Bosch alarm beeping and the DSC PowerSeries trouble light.

Questions to ask your installer

A good handover explains what keeps running locally, what may stop, and how to use the system without the app. “It has a battery” is not enough detail. Ask these questions and write down the answers:

• Which parts of my system have backup power, and for roughly how long?
• What happens to my app and alerts if the router loses power?
• Do I have a mobile SIM path, is it switched on and who pays for it?
• Can you run a test of the backup and show me the result?
• When was each battery fitted, and when should it be checked or replaced?
• Who receives the fault alert, and what if that person is away?

Write the answers for a power cut, a broadband failure and a low battery warning as three separate notes. Also show any house sitter or relative how to use the keypad. They may not know that the local controls still work when the app does not.

When an upgrade makes sense

Start with the gap you need to close. A worn backup battery needs a test and a replacement. An alarm that depends on the router alone may need a mobile SIM path. A home that relies only on the phone may just need a keypad and a short lesson.

Compare quotes on the functions they keep running, not on the number of batteries. Ask about ongoing charges, which services are supported and how it is maintained. Ask whether backup for the router and the nbn connection box is part of the quote or a separate job. Powering the router does not fix a failed panel battery, and a new panel does not fix a router with no backup.

FAQ

Sources and further reading

• Ajax Systems: How an Ajax system operates in case of a power outage (source of the hub backup times, Battery Power Saver figures, the delay setting and the NVR and camera notes)
• nbn: Battery back-up information (source of the five hour figure and the June 2024 change)
• nbn: Security alarms and the nbn network (source of the questions to ask your alarm provider)

Ajax figures are the maker’s “up to” times for its own hubs under its stated test conditions. Other brands will differ. The nbn figure applies to fibre to the premises with a battery unit fitted. The router and example points are our general explanation, not a promise for your system. Last checked 13 October 2026 by Sergi Sipko, licensed security installer, Security Adviser and Equipment Installer Licence Z47-808-30S.

Get your outage plan checked

If you are not sure what your alarm does in a blackout, ask SIPKO for a security system maintenance review. We check the backup batteries, the communication path and the router dependency, and give you a short written plan. If you want your system watched around the clock, see our alarm monitoring service.

Serhii Sipko – Melbourne Security Installer

Serhii Sipko is the founder of SIPKO Security and a Melbourne-based security installer specialising in high-quality CCTV systems, security alarm systems, intercoms and integrated electronic security solutions for residential and commercial properties. Based in Melbourne, Victoria, Serhii works with homeowners, businesses, property managers, builders and commercial clients to design, install, upgrade and maintain professional security systems. His work focuses on reliable equipment, careful system design, professional installation and long-term performance rather than simply installing the cheapest available security products. Through SIPKO Security, Serhii provides security system solutions including CCTV camera installation, IP security cameras, network video recorders (NVR), security alarm systems, Ajax alarm systems, access control, video intercoms, security system upgrades, repairs, troubleshooting and ongoing maintenance. Serhii has particular experience with professional security technologies and regularly works with leading security brands and platforms used in residential and commercial security installations. He takes a practical approach to selecting security equipment, considering factors such as property layout, camera coverage, image quality, night-time performance, network infrastructure, alarm detection, remote access and the specific security requirements of each property. As a Melbourne security installer, Serhii provides services across Melbourne and surrounding suburbs, including premium residential areas and commercial locations throughout metropolitan Melbourne. His approach is focused on delivering discreet, professionally designed security systems that integrate effectively with the property and provide reliable protection. Serhii also shares practical security advice and technical knowledge through the SIPKO Security website and blog. His articles cover topics such as CCTV installation in Melbourne, choosing security cameras, security alarm systems, Ajax security systems, commercial security, residential security, intercom systems, security system maintenance and improving the overall security of a property. The SIPKO Security blog is written to provide practical information based on real-world security installation experience. Serhii's goal is to help Melbourne homeowners and businesses make informed decisions when selecting security equipment, planning CCTV coverage, upgrading existing alarm systems or choosing a professional security installer. Serhii Sipko is associated with SIPKO Security, a Melbourne security company providing professional security installation and electronic security services. His professional focus is on quality, reliability, technical knowledge and delivering security solutions that are appropriate for the individual property and client requirements. For clients looking for a professional security installer in Melbourne, Serhii Sipko and SIPKO Security provide CCTV installation, alarm systems, intercoms and integrated security solutions for residential and commercial properties across Melbourne, Victoria.

See Full Bio