Source note. This article is based on the Fire Industry Association's published summary of the changes, Guide to the changes in BS 5839-1:2025 (Version 1, June 2025). It has not been checked line by line against the text of BS 5839-1:2025 itself, which is the authoritative document. Check clause wording in the standard before relying on it in a contract, certificate or dispute. The standard applies to the UK; other countries use different codes.
Why this changed
The FIA guide ties this change directly to the planned 2027 switch-off of the UK's public switched telephone network (PSTN) and the wider move to all-IP networks. Alarm transmission equipment can no longer assume a PSTN path is available, so BS 5839-1:2025 sets out explicit timing criteria the equipment should meet, aimed at keeping the summoning of the Fire and Rescue Service (FRS) reliable and timely regardless of the transmission path used.
The FIA guide also notes that while the 2017 edition already recognised the use of Intruder and Hold Alarm Systems (I&HAS) transmission equipment for this purpose, it did not specify what Grade of signalling that equipment should meet.
The new timings
The FIA's summary reports two sets of maximum timings, split by system category:
- Category L systems. In the event of a fire alarm signal, an indication should be received at the ARC within a maximum of 90 seconds. A catastrophic failure of the transmission system — meaning no alarm signals can be transmitted at all — should be indicated at both the ARC and the control and indicating equipment (CIE) within 3 minutes.
- Category P systems. In the event of a fire alarm signal, an indication should be received at the ARC within a maximum of 120 seconds. The FIA guide states the catastrophic-failure indication timing for Category P as 31 minutes — markedly longer than the Category L figure, consistent with P systems generally protecting property rather than life safety directly.
The guide also describes a recommendation that where a separate power supply unit powers the alarm transmission equipment, it should conform to BS EN 54-4 or BS EN 50131-6 Grade 4.
The new false-alarm test notice
A recurring cause of false Fire and Rescue Service attendances is a system being tested without the ARC being told first. The FIA guide describes a new recommended label, fixed on or adjacent to the CIE, reminding premises management that the system has an active ARC connection to the FRS — a low-cost, practical prompt intended to catch this specific failure mode before it generates a call-out.
More information reaching the ARC
With FRS services increasingly operating call-challenging policies to cut false-alarm attendances, the FIA guide reports a new recommendation that the ARC should hold all relevant information about a premises — for example, whether it contains sleeping accommodation — so that it can be passed on to the FRS. The guide also notes that with all-IP networks and connected technology, it is now practical to transmit more than a bare signal: where practicable, the alarm signal to the ARC should indicate the nature of the triggering device and whether coincidence filtering is in place.
What this means for engineers now
- If you specify or install alarm transmission equipment, check the manufacturer's stated signal and catastrophic-failure timings against the figures above before assuming 2025-edition compliance.
- Confirm what happens to the existing PSTN-based transmission path on a system you maintain, and whether the client has a migration plan ahead of the 2027 switch-off — this is a conversation worth having well in advance, not at cut-over.
- Check whether the CIE already carries a false-alarm test notice, and whether your service documentation captures the premises information (such as sleeping accommodation) the ARC should hold.
See also BS 5839-1:2025 servicing intervals and reducing false alarms.
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Scope
This article covers BS 5839-1 as used in the UK. Alarm transmission and ARC requirements in Ireland, the United States, Canada, Australia and New Zealand are set by different standards and local arrangements, and are not covered here.