Quick answer
If your intruder or fire alarm signals to a monitoring centre over a phone line, that signalling path stops working when the PSTN is switched off on 31 January 2027. The replacement is IP-based signalling, usually dual-path (broadband plus a mobile connection) so a single failure cannot silence the alarm. This work must be done by your alarm company, not your phone provider, and it may need re-commissioning and re-registration with the monitoring centre. Book it now: alarm engineers are the bottleneck in this whole migration, and their diaries fill before the deadline does.
Of everything the switch-off touches, alarms are where I see the most dangerous assumption: that because the alarm still makes a noise, it is still working. A monitored alarm has two jobs - make a noise locally, and tell somebody. The switch-off breaks the second one silently. The bells will still ring on 1 February 2027. Nobody will be told. And if your insurance policy specifies a monitored alarm, the gap between those two facts is a coverage problem as well as a security one. If you need the phone lines sorted alongside this, get a no-obligation quote - but call your alarm company first, and read on for what to ask them.
How your alarm uses the phone line
Most business alarm panels installed before roughly the mid-2010s report to an alarm receiving centre (ARC) using a device that dials out over the analogue line - a digital communicator, often just called a dialler. When a zone is triggered, the panel seizes the line, dials the centre and sends a coded message. The centre then follows your agreed response: call your keyholders, call a guarding company, or in some cases notify police. There were also dedicated monitored signalling products delivered over the phone network - BT RedCARE being the best known - which added line-monitoring so that cutting the line itself raised an alarm. These legacy PSTN-based products are being retired alongside the network they depend on.
The awkward part is that many business owners genuinely do not know which they have. The panel is in a cupboard, the contract renews annually, and the last engineer visit was a service call. Two quick tells: a phone cable running into the alarm panel or a nearby junction box means line-based signalling, and a line on your bill that nobody can account for is quite often feeding the alarm. Our guide to devices that rely on phone lines covers the wider audit.
First, work out which kind of alarm you have
| Type | How it behaves | Switch-off impact |
|---|---|---|
| Bells-only / local sounder | Makes noise on site, tells nobody remotely | None from the switch-off itself, unless it uses a line for engineer access |
| Monitored intruder alarm | Signals to an ARC over a phone line | Signalling path fails - alarm sounds, nobody is notified |
| Monitored fire alarm | Signals fire and fault conditions to an ARC | Same, with life-safety and regulatory consequences |
| App-only / self-monitored | Notifies you over the internet | Usually unaffected, but check whether the panel also dials out as a backup |
| Police-response system | Monitored to a defined standard with a URN | Signalling must meet the required grade or response can be withdrawn |
If you are in the bottom three rows, this is urgent. If you are bells-only, you have less to do - but still check whether the panel has a line for remote engineer access, because losing that means every future change becomes a site visit.
What replaces PSTN alarm signalling
| Replacement | How it works | Best for | Trade-off |
|---|---|---|---|
| Dual-path (IP + mobile) | Signals over your broadband, with a mobile radio path as backup | The default for monitored commercial systems | Highest cost; needs a working broadband connection |
| Single-path IP | Signals over your broadband only | Lower-risk sites, lower grades | One failure point - broadband down means no signalling |
| Mobile-only (GSM/radio) | Signals entirely over a mobile network | Sites with poor or no broadband | Depends on mobile coverage at the panel's location, often indoors |
| App-based self-monitoring | Notifies you directly over the internet | Small sites with no insurance requirement | You are the monitoring centre; no ARC, no police response |
For most monitored commercial premises the answer is dual-path, and that is not upselling - it is the point. A monitored alarm exists to tell someone when something is wrong, so a signalling path that shares a single failure mode with your office broadband is a poor design. Dual-path means an intruder cutting your internet, or a router failing at 2am, does not also disable the reporting.
Note what this means practically: your alarm will now often depend on the same broadband your phones use. That makes your connectivity choice and its resilience more important than it was. See SoGEA vs FTTP for business for what you can get, and landline resilience and failover for keeping it up.
The insurance and standards angle
This is the part that decides the specification, and it is worth getting in writing.
UK commercial intruder alarms are typically installed to recognised standards, with the signalling path itself graded according to how quickly a fault or a cut path must be detected and reported. Your alarm company will know which grade your system was certified to and what the equivalent IP-based grade is. Do not let anyone downgrade it as a cost saving without telling your insurer.
Three practical actions:
- Read your policy wording. Many commercial policies require a monitored alarm, sometimes to a named standard, sometimes with a specified response. A system that no longer reports may not meet the condition.
- Get the new specification in writing from your alarm company, including the signalling grade, and keep the certificate.
- Tell your insurer what changed once it is done. A short email with the certificate attached is usually all that is needed, and it removes any argument later.
If your system has a police URN, the required signalling standard is not negotiable - falling below it can mean losing police response, which is very hard to get reinstated.
Fire alarms and other life-safety signalling
Monitored fire alarm systems follow the same technical path but carry more weight. Where a fire alarm reports to an ARC, that reporting is often part of a regulatory or insurance obligation rather than a convenience, and the record-keeping matters. Treat it as a separate line item from the intruder alarm, arranged with whoever holds the fire alarm maintenance contract, and make sure the change is logged in your fire safety documentation.
The same applies to other signalling you may not think of as an alarm: sprinkler and suppression monitoring, cold-store and plant-room temperature alarms, plant telemetry, and gas detection. Anything that quietly phones somebody when a threshold is crossed is in scope. Sites with care or telecare lines have additional requirements again - see the switch-off in care homes and telecare settings.
The one thing not to do
Do not plug an existing alarm dialler into a digital voice line or an analogue adapter and consider the job done.
It is a tempting shortcut, and it will often appear to work - you can dial out, and a test call may complete. The reasons it is unsafe are specific. Older diallers use signalling tones and timings designed for the analogue network, which do not always survive the conversion reliably; the adapter and router lose power in an outage where the old line did not; and, most importantly, nothing tells you when it has stopped working. An alarm signalling path that fails silently is worse than no signalling path at all, because you believe you are covered.
If a phone engineer offers you this as a solution, decline it and call your alarm company. This is genuinely their trade, and the equipment they fit is designed to supervise itself and report its own faults.
Who does what, and how long it takes
| Task | Who | Typical lead time (as a guide, August 2026) |
|---|---|---|
| Identify the panel and current signalling | Your alarm company | Days |
| Quote and specify the replacement path | Your alarm company | Days to weeks |
| Fit and commission new signalling | Your alarm company | 4-12 weeks from order - engineer availability, not hardware |
| Re-register with the monitoring centre | Alarm company with the ARC | Included, but must be confirmed in writing |
| Provide the broadband the signalling will use | Your telecoms provider | 2-6 weeks for FTTP or SoGEA |
| Cease the old alarm line | Your telecoms provider | Only after the new path is confirmed working |
Read that table from the bottom up and the sequencing becomes obvious: the broadband has to exist before the alarm can use it, and the alarm has to be proven before the old line is ceased. That is why our switch-off deadline guide puts the alarm phone call in week one, ahead of any decision about handsets.
What it costs
We will not invent a figure, because this varies more than anything else in the migration - it depends on the panel's age, whether it can accept a modern signalling module at all, the grade required, and whether the monitoring contract is renegotiated at the same time. As a guide, expect a one-off equipment and commissioning charge per panel plus a monthly signalling and monitoring fee, with the one-off likely to be one of the two largest single items in your whole project. The other is the lift.
Two ways to keep it honest: get a written quote separating equipment, labour and ongoing monitoring, and check whether your monitoring contract's renewal date is being quietly bundled into the deal. Our switch-off cost guide covers the rest.
Five questions to ask your alarm company
- Does our panel signal over the phone line, and what product or path does it use today?
- What grade of signalling is our system certified to, and what is the equivalent IP-based specification?
- Is the replacement single-path or dual-path, and why is that right for this site?
- What is the total one-off cost, the new monthly cost, and the earliest engineer date?
- Will you confirm in writing that the new path is commissioned, tested and re-registered with the monitoring centre?
Get question five answered on paper. It is the document you will want if you ever need to make a claim.
The bottom line
A monitored alarm on a phone line is the switch-off risk most likely to be missed, because nothing visible changes until the day you need it. The alarm will still sound; it will simply stop telling anyone. Fixing it is routine work for your alarm company, needs a dual-path IP signalling upgrade in most commercial cases, and takes several weeks that are getting harder to book. Make that call this week, get the specification and the commissioning confirmation in writing, and tell your insurer when it is done.
If your alarm sits on a line you also need replacing, we can handle the connectivity and voice side around your alarm company's schedule: get a no-obligation quote or call 0333 006 9399.
Getting unknown calls on a business line? Our free UK phone number checker shows which network or provider Ofcom allocated any number to, and whether the range is in service — no sign-up.
Frequently asked questions
Will my alarm still work after the PSTN switch-off?
The alarm will still detect and still sound, but if it signals to a monitoring centre over a phone line, that reporting stops. That is the dangerous part - the failure is invisible from inside the building, so a system that looks fine is no longer telling anyone when it triggers.
What replaces phone line alarm signalling?
IP-based signalling, usually dual-path: your broadband as the primary route with a mobile radio path as backup, so one failure cannot silence the alarm. Single-path IP or mobile-only options exist for lower-risk sites or premises with poor broadband, and your alarm company will specify what your grade requires.
Who is responsible for upgrading my alarm signalling?
Your alarm company, not your telecoms provider. The work involves the panel, the signalling module and re-registration with the monitoring centre, all of which sit inside the alarm installer's remit. No phone provider's migration plan includes your alarm.
Can I plug my alarm dialler into a digital phone line?
You should not treat this as a solution. Older diallers rely on analogue signalling behaviour that does not reliably survive conversion, the adapter loses power in an outage where copper did not, and nothing reports the failure. A signalling path that fails silently is worse than none, because you believe you are protected.
Does the switch-off affect my insurance?
It can. Commercial policies often require a monitored alarm, sometimes to a named standard with a specified signalling grade. If the alarm stops reporting, you may not be meeting that condition. Check your policy wording, keep the new certificate, and send your insurer confirmation once the upgrade is complete.
How long does an alarm signalling upgrade take?
Typically four to twelve weeks from order as a guide, and the constraint is engineer availability rather than equipment. Availability tightens as the deadline approaches, which is why this should be your first phone call rather than something you fit around the phone system decision.
What about my fire alarm and other monitored systems?
The same applies, with more at stake. Monitored fire alarms, sprinkler and suppression monitoring, temperature and plant alarms, gas detection and telecare all signal over lines and all need their own plan with their own maintainer. Log each change in your fire safety and compliance records.