How do I reduce false alarms on a fire alarm system?

Direct answer

BS 5839-1 divides false alarms into unwanted alarms (a response to a fire-like phenomenon, environmental influence, accidental damage or inappropriate human action), equipment false alarms, malicious false alarms and false alarms with good intent. Most are unwanted alarms, and most of those can be reduced by choosing the right detector type for each area, siting detectors correctly, managing work in protected areas, keeping the system maintained, and investigating and recording the cause of every false alarm.

Applies to

• Products / Models: All Hochiki Europe detectors and panels (general guidance)

• Firmware / Version: Not applicable

• Region: UK

• Standards: BS 5839-1 (false alarm and unwanted alarm management)

Common causes

• Cooking fumes, steam and high humidity near optical smoke detectors.

• Dust and aerosols, insects, or condensation in the detector chamber.

• Detector type or siting not suited to the environment.

• Lack of maintenance or contamination over time.

• Malicious or accidental operation of manual call points, particularly in premises the public can access.

How to reduce false alarms

1. Select the appropriate detector type for each area

   • Consider a heat detector first. BS 5839-1 recommends confirming that a heat detector would not meet the objectives of the system before another detection principle is used, because heat detectors give rise to lower rates of unwanted alarms in most premises. Do not use a rate-of-rise heat detector where the temperature fluctuates rapidly, such as a kitchen, boiler room or loading bay.

   • Where smoke detection is still needed in an area prone to transient smoke or steam, select the detector and its mode of operation together. BS 5839-1 warns that having more than one sensor in a detector does not, on its own, necessarily reduce unwanted alarms; the benefit depends on how the signals are combined. Hochiki multi-sensor detectors such as the ACD-EN combine optical, heat and CO sensing elements and offer 24 EN-approved modes of operation, so the mode chosen for each area matters as much as the detector type. Agree the mode with a competent person and record it.

2. Site detectors correctly

   • Keep detectors away from sources of steam, fumes, dust and rapid air movement.

3. Protect manual call points

   • BS 5839-1 recommends that all manual call points are fitted with a protective cover that is moved to gain access to the frangible element. That recommendation is not retrospective, but covers should also be fitted to existing systems in which unwanted operation of manual call points is frequent.

   • Do not site manual call points where they are exposed to impact from trolleys, forklift trucks or ball sports; fit guards where the siting cannot be changed.

4. Maintain the system

   • Follow the manufacturer's recommended servicing schedule together with the inspection and servicing regime in BS 5839-1, which recommends that the period between successive inspection and servicing visits should not exceed six months; clean or replace contaminated detectors promptly.

5. Investigate and record every false alarm

   • Record, for every false alarm: date and time; the device and its location; the category of false alarm; the reason (or the activity in the area if the reason is unknown); the action taken; whether the fire and rescue service were called and whether they attended; and who recorded it.

   • Ask your service provider to carry out a preliminary investigation if any of the following apply: the rate over the previous 12 months exceeds one false alarm per 25 detectors; 11 or more false alarms have occurred since the previous service visit; two or more false alarms, other than false alarms with good intent, have come from the same call point or detector (or detector location) since the last service visit; a persistent cause has been identified; or more than two unwanted fire alarm signals have occurred in the previous 12 months.

   • Commission an in-depth investigation by a specialist if, in any rolling 12 months, a system with more than 40 detectors exceeds one false alarm per 20 detectors, or three or more false alarms come from a single device; for systems with 40 detectors or fewer, if three or more false alarms occur.

6. Manage work in protected areas

   • Tell occupants, and any alarm receiving centre the system reports to, before any test or maintenance that could produce a fire signal. Contact the alarm receiving centre immediately before and immediately after the weekly test.

   • Operate a permit to work system for hot work, dust, paint spray or similar work in areas protected by smoke detectors, and use temporary covers, screens or a planned disablement — then confirm the protection has been reinstated.

   • Fix building and plant defects that cause unwanted alarms, such as leaking roofs, steam leaks and inadequate ventilation.

7. Review system features

   • Only after the steps above have been exhausted, ask a competent person whether filtering measures are appropriate. BS 5839-1 recommends adopting filtering — such as reduced sensitivity at certain times, a time-related mode or a staff alarm investigation period — only where false alarms cannot be brought to an acceptable level by other means and where filtering does not defeat the objectives of the system. Filtering should not be applied to signals from manual call points, heat detectors or sprinkler systems. Where a sensor in a multi-sensor detector is disabled or desensitised at certain times, the detectors need to be sited for the least sensitive sensor that remains active. Record any change and the reason for it. Where a change of detector sensitivity or heat threshold is being considered as part of this review, see How do I change the sensitivity or heat threshold on an ALN-EN or ACC-EN sensor?.

When to contact technical support

• If false alarms recur from the same device or area after the steps above.

• If you need advice on detector selection or sensitivity configuration.

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 (verify current edition with BSI) — Fire detection and fire alarm systems for buildings: Code of practice for design, installation, commissioning and maintenance (includes false alarm management guidance)

• Relevant detector data sheets (sensitivity / mode options)

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