A phone-line change with a security consequence
Many older intruder alarms report to a monitoring centre through the household telephone line. The traditional landline network, the Public Switched Telephone Network (PSTN), is being retired across the United Kingdom, and phone services are moving onto broadband. This article summarises GOV.UK guidance published on 28 May 2025, Ofcom’s consumer page on the switchover (last updated 26 August 2026) and National Security Inspectorate (NSI) advice for alarm owners. The change is UK-wide, although the timetable depends on which network carries the line.
What the timetable says
GOV.UK states that the telecommunications industry is switching off the PSTN by January 2027 and that devices reliant on it, including alarm systems, telecare devices and door entry systems, will need upgrading. It reports that over two thirds of UK landlines had already moved to internet-based voice services when the page was published.
Ofcom is more specific about networks. It says BT plans to retire its old landline network by 31 January 2027, so that customers of providers using the Openreach network should by then have moved to a digital landline or an alternative service. It adds that other companies with their own networks, including Virgin Media O2 and KCOM, also plan to retire their old networks but that dates for those had not been set.
Why an alarm may be affected
A digital landline works over a broadband connection. Ofcom explains that the phone is plugged into the broadband router rather than the wall socket. GOV.UK says that some people without broadband will be offered an interim dedicated landline service that lasts until a digital solution is available or until 2030, if that comes sooner.
The NSI, a certification body for alarm installers, explains the alarm-specific consequence. When a home moves to a digital service, a traditional telephone connection, including an intruder alarm, may no longer be able to send signals. The NSI says some alarm systems that use analogue telephone lines may not work on the digital service, others may work after minor modifications, and the alarm will likely need reconnecting once the phone service changes. It also stresses that not all systems will be affected and that replacement is not automatically needed.
The scale of the task was recognised early. In September 2023 the British Security Industry Association (BSIA) estimated that more than one million PSTN-connected alarm systems in the UK had not yet transitioned, and that many owners might be unaware changes were needed. That figure is a 2023 estimate, not a current count.
Who to tell, and when
Ofcom asks customers to tell their phone provider before the change if they have a care alarm, health pendant, security alarm or other connected device that uses the phone line. GOV.UK gives similar advice and adds that anyone buying a new alarm should check with the equipment supplier that it is compatible with digital phone lines.
The NSI advises contacting the alarm or maintenance provider before the line is upgraded, to find out whether the alarm needs adapting or replacing. If an alarm company proposes an upgrade, the NSI recommends asking for a detailed quote that explains why the change is necessary. Owners can also use the checks in Monitored Alarm Standards and Accreditation: Evidence Checks to confirm that a proposed installer is independently certified.
Power cuts and the digital line
Ofcom states that digital landlines need mains electricity and will not work in a power cut unless there is a battery back-up. It says that a customer who depends on the landline and lacks a working mobile phone or reliable mobile signal must be offered a free back-up solution that lasts at least one hour, with some providers offering up to seven hours. That requirement concerns access to emergency services, not the operation of an alarm signalling path, so an alarm’s own battery and communicator design still matter. The wider picture of outage risk is set out in Alarm Communication Failures: Broadband, Mobile and Power Outages.
A practical sequence
- Establish whether the alarm signals over the phone line, or uses a broadband or mobile communicator.
- Ask the alarm provider, in writing, whether the panel and communicator will work on a digital landline.
- Tell the phone provider about the alarm before any migration date.
- Test the alarm’s signalling after the migration and confirm with the monitoring provider that a test signal arrived.
- If a problem follows, contact the phone provider first. Ofcom says complaints can go to an alternative dispute resolution scheme if unresolved after six weeks or after a deadlock letter.
The bottom line
The retirement of the analogue phone network is a scheduled, UK-wide change, and BT’s network is due to be retired by 31 January 2027. An intruder alarm that signals over a landline can stop reporting without any visible fault, so the sensible course is to identify how the alarm communicates, ask the installer whether it is compatible, tell the phone provider before migration and test the signal afterwards. The NSI states that replacement is not necessarily required, and a written quote explaining any proposed upgrade is a reasonable request.
Sources
- GOV.UK, Department for Digital, Culture, Media and Sport and Department for Science, Innovation and Technology, “Moving landlines to digital technologies”
- Ofcom, “Your landline is going digital: what you need to know”
- National Security Inspectorate, “UK transition from analogue to digital landlines”
- British Security Industry Association, “Installer toolkit developed to encourage end users to ‘Beat the Big Switch Off’” (27 September 2023)