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What is the difference between a detection zone and an alarm zone?

A detection zone says where a fire has been detected; an alarm zone says where the alarm is sounded, and one alarm zone may contain several detection zones.

Direct answer

A fire alarm zone is a defined area of a building that the panel indicates separately, so that the fire can be located quickly and people can be evacuated and directed. BS 5839-1 distinguishes a detection zone (the area covered by a group of detectors/call points shown as one location on the panel) from an alarm zone (the area within which the alarm signal is broadcast, used in phased or staged evacuation). The exact rules — such as maximum zone area, search distance and how zones relate to building layout — should be taken from the current BS 5839-1 and applied by a competent designer; this article explains the concept, not the limits.

Applies to

  • Products / Models: Not applicable (a system design concept)
  • Firmware / Version: Not applicable
  • Region: UK
  • Standards: BS 5839-1 (zoning)

Why are buildings divided into zones?

  • When the panel signals a fire, staff and the fire service need to find the source quickly. Zones narrow the search to a defined area.
  • On a conventional system the zone is what the panel can indicate; on an addressable system the panel can indicate the individual device, but zones are still defined for clear, consistent indication and for the building plan. BS 5839-1 recommends that zone indication be given at the panel even when addressable text information is also available.

Detection zone and alarm zone compared

  • Detection zone — the geographical area monitored by a group of detectors and manual call points that the panel reports together as one location. It answers "where has something been detected?".
  • Alarm zone — the area within which the alarm warning is given. In a simple building the whole building is one alarm zone; in larger or phased-evacuation buildings the building is divided so that some areas are alerted before others. It answers "where is the alarm being sounded?". Because occupants of neighbouring alarm zones are expected to stay in the building while one zone evacuates, BS 5839-1 recommends that the boundaries of every alarm zone other than external walls comprise fire-resisting construction. Where appropriate, the configuration of alarm zones should be approved by the relevant enforcing authority (BS 5839-1).
  • A detection zone and an alarm zone are not always the same area, but the relationship runs one way only: an alarm zone may contain more than one detection zone, and not the other way round. BS 5839-1 also recommends that the boundaries of alarm zones coincide with the boundaries of the relevant detection zones.

How are fire alarm zones defined?

  • A competent designer defines the zones from the building layout, its use and the evacuation strategy, in line with the current BS 5839-1. See What is a competent person for fire alarm work?.
  • BS 5839-1 places limits on things such as the floor area of a detection zone and the "search distance" — the distance someone has to travel inside the zone before they can see where the fire is (not the distance to the fire itself). On an addressable system the search-distance limit can be relaxed where the panel gives a clear text location for the first device to respond and firefighters unfamiliar with the building could act on it. The precise figures and conditions come from the current BS 5839-1, not from a general article.
  • The zone plan is documented (often as a zone chart displayed at the panel) and confirmed at commissioning and handover — see Fire alarm commissioning and handover: what to expect.

How do zones relate to the system category?

  • Zoning works alongside the system category (what the system is designed to protect and how much of the building it covers) — see Fire alarm system categories explained (BS 5839-1: M, L and P).
  • Changing the building layout or use can change both the zoning and the category; review them together with a competent person.

When should you contact technical support?

  • If you need to understand how your Hochiki panel indicates zones or how many zones it supports.
  • If a building change means the zone plan may need revising — this requires a competent designer, not a general article.

Safety note

This article is general guidance for Hochiki Europe products. Design, installation, commissioning, maintenance and modification of fire detection and alarm systems should be carried out by, or under the responsibility of, a competent person in accordance with the applicable standards (for example BS 5839-1 in the UK). Statutory requirements imposed by the relevant enforcing authority also apply. Always refer to the current product manual and data sheet for the exact model before carrying out any work.

References

  • BS 5839-1 (current edition) — detection zones, alarm zones and zoning recommendations
  • The system's zone plan / zone chart

Last reviewed: 2026-10-21 — Reviewed by: Hochiki Europe Technical Support