- Many monitored alarm systems use the PSTN to dial an alarm receiving centre, and that copper signalling path is withdrawn as the network moves to all-IP.
- Openreach's all-IP migration is scheduled to complete in 2027, after which alarm communicators that rely on the analogue PSTN will no longer signal reliably.
- A digital voice line is not guaranteed to carry the data tones older alarm communicators use, so plugging the alarm into the new router may not work.
- Replacement signalling uses IP or mobile paths, often a dual-path communicator that combines broadband and a mobile network for resilience.
- Responsibility for checking and upgrading the alarm sits with the alarm company or installer, not the broadband provider, so contacting them is the first step.
If your monitored alarm dials out over the old phone line, it may stop signalling after the PSTN switch-off. Contact your alarm company to check the communicator and upgrade it to IP or mobile monitoring.
Last reviewed: June 2026
How most home alarms use the phone line
A burglar alarm that only makes a noise is a local alarm; a monitored alarm does something more. When it is triggered, it sends a signal out to an alarm receiving centre, which then follows an agreed procedure such as calling a keyholder or, in some cases, requesting a police response. For decades the simplest way to send that signal was over the telephone line. The alarm panel included a communicator that picked up the line and dialled the monitoring centre, transmitting a short burst of data tones to report the event. That copper line was reliable, always present and powered from the exchange.
This is precisely the arrangement that the move to all-IP disrupts. The signalling path that older alarms depend on is the analogue PSTN, and as that network is retired the tones the communicator sends may no longer be carried in the way the alarm expects. Even where a digital voice line is fitted, it is not guaranteed to support the old data signalling, because digital voice is engineered to carry speech rather than the precise tones an alarm dialler uses. The result is that a monitored alarm can appear to work locally while silently failing to reach the monitoring centre.
Why the PSTN switch-off affects alarms
The Public Switched Telephone Network is the legacy analogue system, and it is being withdrawn as Openreach migrates the country to all-IP. Openreach's published programme schedules the all-IP migration to complete in 2027. After that point, services that relied on the copper PSTN are delivered digitally over broadband instead. For a voice call the change is largely seamless, but for a device that was designed to transmit data over the analogue line the change can be significant.
The risk is that an alarm continues to behave normally day to day, arming and disarming and sounding its siren, while its ability to call the monitoring centre has quietly stopped working. Because that signalling failure is invisible during normal use, it may only come to light during an actual alarm event, which is the worst possible moment to discover a problem. This is why the switch-off is treated as an urgent prompt to review any monitored alarm rather than a change that can be left until something breaks.
Home alarm PSTN migration options
The way forward depends on the age and type of the system and how it is currently monitored. The table below sets out the common migration options. Costs are described in general terms because they vary by installer, system and contract; an exact quotation should come from the alarm company.
| Option | How it signals | Resilience | Cost guide |
|---|---|---|---|
| IP communicator | Signals over the broadband connection | Depends on broadband and power | Module plus installation, varies |
| Mobile (GSM) communicator | Signals over a mobile network | Independent of home broadband | Module plus ongoing connectivity |
| Dual-path communicator | Combines broadband and mobile paths | Highest, falls back if one path fails | Higher hardware and monitoring fee |
| Full system replacement | New IP-ready panel and communicator | Modern, matched to current standards | Largest outlay, whole new install |
For many monitored installations a dual-path communicator is favoured because it does not rely on a single connection: if the broadband fails, the mobile path can still send the signal, and vice versa. The choice ultimately depends on the alarm company's assessment of the system and any insurance or grading requirements that apply to the property.
What to do and how urgent it is
The first and most important step is to contact the alarm company or installer that maintains the system. They can confirm how the alarm currently signals, whether it uses the PSTN, and what upgrade the panel needs. If the original installer is no longer trading, any reputable alarm maintenance company can carry out the same assessment. The broadband provider cannot do this for you, because they do not know how the alarm is wired or monitored; the alarm is a separate contract and a separate piece of equipment.
On urgency, the safest approach is to act well ahead of any line migration rather than waiting until the switch happens. Migration is being rolled out across the country in stages, and a household may be moved to a digital line before the national 2027 completion date. Because a signalling failure is invisible during normal use, leaving the check until later risks discovering the problem during a real incident. Booking an assessment now, confirming the communicator is IP-ready, and asking the company to test that signals reach the monitoring centre after any line change is the reliable way to avoid a gap in cover.
Insurance and ongoing monitoring
Where a monitored alarm is a condition of a home insurance policy, keeping the signalling working is not just a security matter but a contractual one. If the alarm can no longer reach the monitoring centre, the property may not meet the security requirements the insurer set, which is another reason to resolve the communicator before the line changes. The alarm company can advise whether the upgrade affects the system's grading or the monitoring contract.
It is also worth confirming what power resilience the upgraded communicator has, since an IP signalling path depends on mains power and broadband in the same way a digital phone does. Many alarm panels include a standby battery, but the broadband router that an IP communicator relies on may not, so the household should understand how the system behaves in a power cut and whether any additional backup is needed. Treating signalling and power as linked questions gives the most dependable outcome.
Frequently Asked Questions
Will my home alarm still work after PSTN switch-off?
The alarm will still arm, disarm and sound locally, but a monitored alarm that signals over the old phone line may stop reaching its monitoring centre. The local functions do not depend on the phone line, while the remote signalling does. An assessment by the alarm company confirms whether the communicator needs upgrading.
How do I know if my alarm uses the PSTN?
If the alarm panel is connected to a telephone socket or wired into the phone line, it most likely signals over the PSTN. The clearest way to be sure is to ask the alarm company or installer, who can check the communicator type. Older monitored systems installed before the move to IP are the most likely to be affected.
Who should I contact about my alarm and the PSTN switch-off?
Contact the alarm company or installer that maintains the system, not the broadband provider. The alarm is a separate contract and only the alarm company can confirm how it signals and what upgrade is needed. If the original installer has ceased trading, any reputable alarm maintenance firm can carry out the assessment.
What replaces PSTN for alarm monitoring?
Modern alarm signalling uses IP over the broadband connection, a mobile network path, or a dual-path communicator that combines both for resilience. A dual-path option is often chosen because it can fall back to the mobile path if broadband fails. The alarm company recommends the option that suits the system and any grading requirements.
How much does it cost to upgrade an alarm for IP monitoring?
Costs vary widely by installer, system and the type of communicator chosen, and there is often an ongoing monitoring fee on top of the hardware. A communicator module fitted to an existing panel costs less than a full system replacement. Because pricing is system-specific, the alarm company should provide a written quotation for the exact upgrade.
