Does an Alarm or CCTV Work When the Power or Internet Goes Out?

Customers ask me this more than almost anything else, usually in one of two ways: "why do we need a SIM card?" and "we got a new modem and the cameras stopped working". The answers depend on what has gone out, so this page takes each case in turn, for the systems I install: Ajax alarms and Dahua cameras.

First, a power cut takes your internet with it

This is the part most people miss. Equipment connected over the nbn does not work during a power outage, and the Australian Government lists security alarms among the services affected. [F] Your modem needs power, so when the power goes, the internet goes with it.

That is why the power question and the internet question are really one question. An alarm that relies only on your home internet goes quiet on your phone at exactly the moment the house is dark.

Does an Ajax alarm work in a power cut?

Ajax detectors and the wireless sirens run on their own batteries, so a power cut does not touch them. Ajax rates the detector batteries at up to 7 years. [C]

The hub, the box that talks to everything, has a built-in backup battery. On the Ajax Hub 2 (4G) that I install, Ajax gives the calculated battery life as up to 15 hours when the hub is running on its SIM card alone. [A] The hub recharges the battery itself when the power comes back.

So in a normal Perth power outage the alarm carries on as if nothing happened. The question is whether it can still tell you about it, and that comes down to the SIM.

Does an Ajax alarm work without internet?

If the hub loses its connection completely, Ajax says the system keeps working on its own: it responds to every detector, runs its automations and sounds the sirens. [B] The alarm still goes off.

What stops is everything that travels through the internet. You cannot arm or disarm from the app, and the events are stored in the hub and delivered to the app once the connection is restored. [B] A siren going off in an empty street is still a deterrent, but you would not know about it until later.

Why does an Ajax hub need a SIM card?

The Hub 2 (4G) has an Ethernet port and two micro-SIM slots for the mobile network. Ethernet is used first. If it drops, the hub switches to the SIM card instantly, and the channels run side by side so a failure on one does not stop the alerts. [A] The SIM sits inside the hub, so there is nothing extra to mount. The Hub 2 Plus adds Wi-Fi as another path.

With a SIM fitted, a power cut or an internet outage makes no difference to you. The app keeps working and the alerts keep coming. I recommend a backup SIM on every Ajax system, and there are two ways to do it:

• An Ajax SIM. I activate it for you and it costs $120 a year, which you pay me annually.
• A prepaid SIM of your own. I usually suggest an Amaysim prepaid SIM on a long-expiry plan, so it does not need topping up every month.

Not everyone wants one, and the alarm works without it. Just know that without a SIM the hub cannot reach your phone during a power cut. The Bibra Lake workshop is an example with a backup 4G SIM in the hub.

Do security cameras work without internet?

A Dahua camera system records to a hard drive inside the NVR, the recorder. The recorder takes a hard drive of up to 20 TB and records continuously or on motion, whichever is set. [D] None of that needs the internet.

When the internet drops, the cameras keep recording. What you lose is remote viewing: the Dahua app on your phone cannot reach the recorder until the connection is back. The footage is still there to play back afterwards, and you can watch on a screen plugged into the recorder at any time. Some of the Dahua cameras I install also take their own microSD card of up to 512 GB, which records inside the camera as well. [E]

Do security cameras work in a power cut?

This is where cameras differ from an Ajax alarm. The recorder runs from mains power, and it powers the cameras through the same network cable that carries the video. [D] When the power goes, the recorder and every camera go off together, and nothing is recorded until the power returns.

The fix is a UPS, a battery backup that the recorder plugs into. I recommend one on camera systems, although not every customer takes it, for three reasons:

• It keeps the system recording through a short outage.
• It protects the recorder from the spikes that can come when the power returns.
• It saves the hard drive from being switched off suddenly, which is hard on a drive that is recording all the time.

How long a UPS keeps the system running depends on its size and the number of cameras, so I size it to the system rather than quote a figure here.

Do I need one?

Need is a strong word. Your cameras work perfectly well without one until the power goes out, and in most Perth suburbs that is a handful of short outages a year. What a UPS buys you is the outages being the times you are still covered rather than the times you are not, and that matters more on some properties than others.

I would put one on if any of these is true:

• Your power goes out often. Some streets and some rural blocks are worse than others, and you already know which one you are on.
• The cameras are the main thing protecting the property. If there is no alarm, the cameras going dark is the whole system going dark.
• It is a business. A recorder that drops out mid-incident is the one recording you will want and will not have.

On a home with an Ajax alarm alongside the cameras, it matters less, because the alarm keeps running on its own battery and still calls your phone. The cameras are the part that stops.

Put the modem on it too

This is the bit most people miss. A UPS on the recorder keeps the cameras recording, but if the modem is still plugged into the wall it goes off with everything else, and you cannot see any of it from your phone until the power is back. The footage is being saved, you just cannot watch it.

Plug the modem and the router into the same UPS and you keep remote viewing through the outage as well. It is a few more watts on the same battery, so it shortens the runtime, and on most jobs it is worth it. Tell me if you want it set up that way and I will size the UPS for both.

How many boxes you have to cover depends on your connection, and this is the part most people get half right. On fibre to the premises there are two: the nbn connection box on the wall and your own modem or router, and both need power. On fibre to the node there is no nbn box in the house at all. The copper comes to the wall and your modem does the lot, so it is the modem and the recorder on the one UPS. The simple test is whether there is an nbn box on your wall.

Where there is an nbn box, the older ones came with a battery backup of their own, rated at up to about five hours. [G] nbn stopped supplying them in June 2024, and the determination covering backup power offers lapsed on 1 October 2024, so a box installed recently will not have one. [G] [H] You can still source a battery yourself if you would rather cover the nbn box that way than run it off the UPS.

My own place is set up that way. The nbn box is an older model with its own battery, and the gateway sits on the UPS next to the recorder, so the internet and the cameras both ride through an outage and I can still watch the cameras while the street is dark. I set clients up the same way when they want it. A UPS is a small addition to a camera job rather than a project of its own, so ask for it with the quote.

New modem and the cameras stopped working?

This is the other question I get a lot. Your cameras are almost always still recording. The recorder has simply lost its link to the internet through the new modem. In my experience it is one of these:

• The recorder is not plugged into the new modem. The network cable that went into the old modem has to go into the new one.
• The recorder needs a restart. A new modem can hand out a different range of network addresses. The recorder picks up a new address automatically, but it usually needs a restart before it does.
• A range extender lost its connection. In apartments and double-storey homes where I cannot run a cable back to the modem, I use a range extender with a network port. When the modem changes, the extender has to be connected to the new one.

If none of those bring the cameras back, give me a call and I can sort it out.

When both are out

A power cut on the nbn means both at once. For a typical Ajax and Dahua system that looks like this:

• Ajax with a backup SIM: fully working, alerts on your phone, for up to 15 hours on the hub battery. [A]
• Ajax without a SIM: sirens still sound, but no alerts until the power and internet return. [B]
• Cameras with a UPS: recording, for as long as the UPS lasts. No remote viewing, because the modem is off.
• Cameras without a UPS: off until the power returns.

So the two upgrades that matter are a backup SIM in the alarm and a UPS on the recorder. You can add either one to an existing system. For prices and what each system includes, see Ajax alarm systems and CCTV installation in Perth, or if you want both in one job, an Ajax alarm with Dahua cameras. Every price, including the SIM, is in what an alarm or CCTV system costs in Perth.

Common questions

Sources

1. Ajax Systems, Hub 2 (4G) technical specifications. ajax.systems
2. Ajax Systems support, How does the hub operate without the Internet connection?. ajax.systems
3. Ajax Systems, Why Ajax (blackouts and detector batteries). ajax.systems
4. Dahua, DHI-NVR4108HS-8P-AI/ANZ datasheet (PDF). Datasheet
5. Dahua, IPC-HDW3867EM-S-IL datasheet (PDF). Datasheet
6. Australian Government, Power outages and the NBN (May 2020). www.infrastructure.gov.au
7. nbn, Battery back-up information (fibre to the premises). www.nbnco.com.au
8. ACMA, Outdated backup power rules for telcos sunset (September 2024). www.acma.gov.au