How do I know if my alarm uses the phone line?

Ask your alarm installer or monitoring company — that's the reliable answer. As a rough guide: a 'bells-only' alarm that just sounds a siren has no phone line and isn't affected. An alarm that calls you or a keyholder, or that's monitored by an alarm receiving centre, almost certainly signals over a line or network and should be checked. If you're unsure, treat it as needing a check.

Won't my phone provider sort it out when they switch me over?

Don't rely on it. Ofcom asks providers to tell you what to do and to flag connected devices, but the responsibility for making the alarm itself work falls to you and your alarm company. Ofcom's guidance is explicit: inform your alarm provider so they can make the changes or confirm the alarm works on a digital line. The safe move is to start that conversation yourself.

Is this an insurance problem too?

It can be. If your insurer requires a monitored alarm as a condition of cover, an alarm that quietly stops signalling could leave you in breach without knowing it. We can't tell you what your policy says — check it, and if monitoring is a condition, make the switch-off upgrade a priority and keep a record that it's been done.

What about a power cut?

Worth knowing: a digital phone line only works in a power cut if it has battery back-up, and the same caveat applies to anything relying on it. Ask your alarm company how your system behaves on mains and battery after the change — alarm panels usually have their own back-up battery, but how the signalling path holds up in an outage is a question for them.

Will my intruder alarm work after the PSTN switch-off?

Ross Woodhurst

2 min read•Published 13 June 2026•Updated 13 June 2026

The short version

Whether your intruder alarm survives the switch-off comes down to one thing: how it sends its alerts.

Bells-only alarm — it just sounds a siren and isn't connected to a phone line. Unaffected.
Auto-dialler or monitored alarm — it rings you, a keyholder, or an alarm receiving centre when triggered. If it does that over the phone line, it's the kind at risk.

The analogue phone network (the PSTN) is being switched off on 31 January 2027, and Ofcom is clear that security alarms connected to the line may need to be replaced or reconfigured to keep working afterwards. If yours signals over the line and isn't upgraded, it could stop sending alerts — silently.

Why a monitored alarm is the one to worry about

The danger with an alarm that signals over the phone line isn't that it stops making noise — the siren may still sound. It's that the alert to you or the monitoring centre may never be sent. A break-in still triggers the bell, but nobody is told. That's the failure mode to plan around, and it's exactly why you can't just wait and see.

What to do — and who to ask

This isn't a job to do yourself, and it isn't one to leave to your phone company. The order that actually works:

Contact your alarm installer or monitoring company now. Ask the plain question: "When the PSTN switches off, will my alarm still signal — and if not, what needs changing?" They know your specific system; we don't, and nor does a web tool.
Tell your phone provider you have an alarm on the line. Ofcom asks you to flag this before any switch to a digital line, so they can take account of it during the move.
Check your insurance. If a monitored alarm is a condition of your cover, treat the upgrade as a priority and keep a record that it's been done.
Buying a new alarm? Ofcom's guidance is to ask the manufacturer whether it's compatible with digital (VoIP) phone services before you commit.

What this page can't do

It can tell you the deadline and the right questions. It can't confirm whether your specific alarm is safe, tell you which signalling upgrade to fit, or stand in for your installer's or insurer's advice. A monitored intruder alarm is security equipment — get the answer from the people who installed and monitor it, in good time before January 2027, not in the rush as the deadline closes in.

Frequently asked questions

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Last verified: 13 June 2026

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