Will my alarm still work if the power or broadband goes off?

Yes, an Ajax alarm keeps protecting the building through a power cut or a broadband failure, as long as it was set up for one. The hub switches to its own backup battery, the wireless detectors and sirens carry on with their own batteries, and a SIM card takes over when the router goes dark. The weak spot is a hub with no SIM: it still sounds the sirens, but nothing reaches your phone until the internet comes back.

Zenith Security Co. has supplied security equipment from Wolverhampton since 2012 and stocks the Ajax wireless alarm range. Figures below come from Ajax's own pages and from UK sources, named as we go.

What happens when the power goes off?

A power cut affects more than the alarm. The router goes off, and so does a digital landline: Ofcom notes that a VoIP landline, unlike the old copper network, needs power at the property.

• The hub moves onto its backup battery and reports the loss of mains.
• Wireless detectors, keypads and sirens run on their own batteries anyway. Ajax rates the StreetSiren's batteries at up to five years.
• The router stops, so the hub loses its Ethernet or Wi-Fi link. From then on only a SIM card can carry alerts.
• Mains-powered smart devices, such as smart sockets and power relays, stop until the power returns.

What if only the broadband drops?

Ajax's support pages say a hub that loses its link to the Ajax Cloud server carries on by itself. It still reacts to detectors, runs your automation scenarios and sounds the sirens. Events are stored in the hub and passed to the app when the connection returns.

What you lose is remote control: the apps reach the hub through the cloud. Ajax advises keeping a local way to set the alarm, such as a KeyPad TouchScreen (£235.38 inc VAT) or a SpaceControl key fob (£47.31 inc VAT). If the hub has a SIM, it moves to mobile data, the app keeps working, and it can also text and call users if you have switched that on.

How long does each Ajax hub last on battery?

These are Ajax's calculated figures. For the Hub 2 range they assume SIM only, which is the situation once the router is off. Prices are ours, including VAT, with delivery extra, and they can change.

Is 15 hours enough? Not always. Ofgem's review of Storm Arwen found nearly 1 million homes in Britain lost power in November 2021; 82% were reconnected within 24 hours, but nearly 4,000 were without power for over a week. For a rural or often-empty property, plan for more than a day.

Which connections should the hub use?

Ajax recommends switching on every channel the hub supports, with the wired link doing most of the work and mobile data standing by.

• Ethernet as the main link. On the Hub 2 range the switch from Ethernet to SIM is instant.
• Two SIMs on different networks, so one operator's fault does not remove your backup. On its 4G hubs, Ajax says changing from one SIM to the other can take up to four minutes.
• Wi-Fi as an extra on Hub 2 Plus. It shares the router, so it covers a damaged cable but not a broadband fault.
• Keep the router running with a small UPS, such as the APC Back-UPS 700VA with a UK plug.

Mobile masts need power too: DSIT's 2025 guidance says operators may use backup power and generators at masts, so a SIM backup has limits in a long, widespread cut.

Ajax now fits its own multi-network SIM in new hubs, but says it can only be activated where the service is offered. We have not confirmed it for the UK, so plan on your own SIMs.

Is a 2G hub still worth buying?

The entry model, Hub 2 (2G) Jeweller, uses 2G for its SIM backup. Ofcom says UK 3G networks are now switched off and the operators will switch off 2G by 2033 at the latest, some earlier. Ofcom names security alarms among the devices that may still depend on 2G. The 2G hub works well on Ethernet, but its backup path has an end date, so for a new system we would choose a 4G hub.

Can you make the battery last longer?

• Hub 2 and Hub 2 Plus: the 12-24V PSU (type A) (£21.92 inc VAT) fits in place of the built-in mains supply so the hub runs from low-voltage DC, such as a 12 V supply with its own standby battery. The 6V PSU (type A) (£21.92 inc VAT) runs it from a portable battery; Ajax suggests zinc-air alkaline packs.
• Superior Hub Hybrid 2: Ajax's specification gives up to 60 hours from a 7 Ah backup battery running 15 wired devices. We stock 12 V standby batteries in that size. Ajax lists this hub as Grade 3 under EN 50131.
• Range extenders: a ReX 2 (£158.07 inc VAT) has its own backup battery, rated at up to 24 hours, or 12 hours with its Ethernet port in use. Every device that reaches the hub through it depends on that.

What about the phone line?

Ofcom says BT has decided to close its copper phone network by January 2027. On BT Digital Voice the broadband hub must have power for calls to work. Ofcom requires providers to offer a free solution, such as a battery back-up unit, lasting at least one hour for customers who rely on their landline for emergency calls. That protects 999 calls, not alarm signalling. Ajax hubs do not use the landline at all: they signal over Ethernet, Wi-Fi or SIM.

Our take

For most homes and small businesses, pair Ethernet with two SIMs on different networks on a 4G hub: Hub 2 (4G) at £228.45 inc VAT, or Hub 2 Plus (£268.10 inc VAT) to add Wi-Fi. Put the router on a small UPS and fit a keypad or key fob. Then try it: unplug the router and the hub's mains for a few minutes and check the app still reports. If a company monitors the alarm, tell them first. Larger or wired sites suit Superior Hub Hybrid 2 with a 12 V battery; sites with no mains suit Hub BP.

Not sure which hub suits your building? Call us on 01902 902251 or send us a message. We are a supplier, not an installer: we can talk you through the parts, and we can recommend a qualified installer depending on the job and area. We ship nationally to England, Scotland and Wales.

Quick questions

Does an Ajax alarm work without Wi-Fi?
Yes. Most Ajax hubs connect by Ethernet and SIM. With no internet at all the hub still protects the building and sounds its sirens, but you get no app alerts.

Will the siren go off in a power cut?
Yes. Ajax wireless sirens run on their own batteries and the hub on its backup battery.

Do I need a SIM card in my Ajax hub?
It is not compulsory, but without one the hub cannot reach you when the broadband or power is down.

Will the alarm tell me the power has gone off?
Yes, the hub reports loss of mains to the app, as long as it still has a connection. In a power cut that usually means a SIM.

Source: Ajax Systems, Why every system needs a backup and its blackout guide, plus Ajax support and specification pages; Ofgem, Storm Arwen review; Ofcom, 2G and 3G switch-off; Ofcom, landlines and power cuts (2024); DSIT, telecoms resilience guidance; BT, Digital Voice in a power cut.