Is Your Alarm Still Working? PSTN Switch-Off Guide

Here is an uncomfortable question.

When did you last have confirmation that your intruder alarm or fire alarm monitoring is actually communicating with the Alarm Receiving Centre?

Not "the alarm tested fine last month." Not "it went off when I triggered it." But confirmation that the signal pathway from your building to the monitoring centre is intact and functioning right now.

If your system relies on an old BT landline or a legacy signalling service to communicate, there is a real possibility the answer is: you do not know. And in some cases, the system has already stopped communicating entirely.

This is not scaremongering. It is the direct consequence of three overlapping changes to UK telecoms infrastructure that have been rolling out for several years and are now, in 2026, arriving at their most critical phase.

What Is the PSTN and Why Does It Matter for Your Alarm?

The PSTN (Public Switched Telephone Network) is the analogue copper telephone infrastructure that has underpinned voice and data communications in the UK for well over a century.

It is estimated that around four million fire and security systems in the UK communicate to Alarm Receiving Centres using the PSTN network. That is a significant number. And the network those four million systems depend on is being switched off.

The PSTN is failing due to a lack of parts and, increasingly, environmental factors such as storms or heat-related faults. Ofcom reported that 2024 saw a 45 percent increase in the number of PSTN incidents reported.

The final switch-off date for the UK PSTN network is 31 January 2027, by which point every analogue phone line and ISDN connection in the country will permanently cease to function.

Three Changes That Have Already Happened

The PSTN switch-off does not exist in isolation. It is part of a broader shift away from analogue infrastructure, and three specific changes are directly relevant to business alarm systems.

1. BT Redcare Closed in December 2025

This one matters most for businesses with monitored alarm systems, and it is the change that has caught the most people off guard.

BT Redcare was one of the most widely used alarm signalling services in the UK. Thousands of commercial fire alarms and intruder alarms used it to communicate activations to monitoring centres. BT Redcare operations closed in 2025, well before the final 2027 switch-off deadline.

If your alarm uses BT Redcare and you have not migrated to an alternative signalling solution, your system may look operational from the front panel. The alarm will still sound if triggered. But the signal to the monitoring centre, the part that actually calls for help, may not be going anywhere.

Your alarm is, in that scenario, a very expensive noise maker.

2. 2G and 3G Mobile Networks Have Been Switched Off

Many alarm systems, particularly those installed or upgraded in the 2010s, were fitted with GSM communicators that transmitted alarm signals over the 2G or 3G mobile network.

Many legacy alarm communicators and wireless security devices still rely on 2G or 3G connectivity. Some legacy systems will not notify the GSM unit when the SIM card has stopped communicating. This is one of the most common causes of silent system failure in older monitored alarm systems.

"Silent system failure." That phrase deserves emphasis. The system appears to work. It tests fine. The engineer visits and finds no fault on the panel. But the communication path, the thing that actually connects it to help, has gone.

The UK's major mobile networks completed their 2G and 3G switch-offs in 2024 and 2025 respectively.

3. The Digital Stop-Sell Is Already Active

In practical terms, in many exchange areas, the "stop-sell" is already active: meaning no new PSTN or ISDN services can be purchased, and no system takeovers or modifications involving PSTN lines are permitted.

This means that even if you wanted to maintain your existing PSTN-dependent alarm signalling, you may not be able to do so when it next requires modification or takeover by a new contractor.

What Does This Mean for Your Alarm System in Practice?

The practical implications depend on how your alarm system currently communicates. Here is a breakdown by signalling method:

• PSTN only (single analogue phone line): Your monitoring is unreliable at best, absent at worst. This needs upgrading as soon as possible.
• BT Redcare (any variant): Redcare closed in December 2025. If you have not migrated, your monitoring is already gone. Contact your installer immediately.
• 2G or 3G GSM (single path): The mobile networks these communicators relied on have been switched off. An upgrade to a 4G or dual-path communicator is required.
• Dual-path IP and GSM (2G/3G): The IP path may still be functioning, but the 2G/3G backup has gone. You are now operating on a single path, reducing resilience.
• Dual-path IP and 4G LTE: You are in the best position. Your signalling paths are both on infrastructure that remains active.

Alarm Signalling Grades and Why This Matters for Your Insurance

Alarm signalling grades, designated DP1 through DP4, define how quickly a fault in communication between a business alarm system and the Alarm Receiving Centre is detected.

• DP1: Can take up to 25 hours to detect a path failure, now widely regarded as unsuitable for commercial premises.
• DP2: Detection in approximately 31 minutes: an improvement, but still leaves a significant exposure window.
• DP3: Communication failures detected within 4 minutes, the standard for most modern commercial systems.
• DP4: Detection within 3 minutes, the highest resilience grade.

Think about that from a practical standpoint. If your system is running DP1 signalling and the communication path fails at 9pm, you might not know until 10pm the following evening.

What Does a Compliant, Future-Proof Solution Look Like?

A modern, future-proof signalling solution for a commercial or industrial alarm system typically involves:

• Dual-path signalling over IP and 4G LTE: two independent communication paths, providing resilience against either path failing.
• DP3 or DP4 grade signalling: faster fault detection and better insurance compliance.
• A modern digital communicator: the legacy signalling device in your alarm panel will usually need replacing.
• Connection to a BS 5979 Category II compliant ARC: the benchmark for commercial monitoring.

What About Your Fire Alarm?

Everything above applies equally to fire alarm systems that use remote signalling to an ARC or to the fire and rescue service. If your fire alarm uses PSTN-based signalling, the same urgency applies. In some respects, it is even more critical.

Your fire alarm's signalling arrangements should be reviewed as part of your next annual fire alarm service visit at the very latest. If your system is due a service, raise this explicitly with your engineer or include it in your fire and security maintenance review.

Do You Actually Know How Your Alarm Signals?

A significant proportion of businesses have alarm systems that were installed or upgraded several years ago. The business owner knows the system is there, knows it is serviced, and assumes it is working. The specific signalling technology it uses, and whether that technology is still functional, is not something they have ever had reason to think about. That assumption is now risky.

If you are not certain how your system communicates with the monitoring centre, call your installer or maintenance contractor this week. If you do not have a maintenance contractor, that is a separate problem worth addressing, and one we can help with.

Contact FIDEC for a free assessment of your alarm signalling: 0333 3662 007 or info@fidecss.co.uk.