Earlier this year, Euralarm, the leading European trade association for the fire industry, published a White Paper on multi-sensor fire detectors and their role in reducing false alarms. False alarms are a significant issue, leading to unnecessary costs and delayed emergency responses. By improving detection accuracy, multi-sensor technology not only minimizes false alarms but also ensures a faster reaction to real fire events, enhancing overall safety.

However, despite their modern capabilities, multi-sensor detectors still require regular functional testing to ensure optimal performance. To maintain their reliability, it is essential to use the correct test equipment, designed specifically to verify their functionality and accuracy. Proper testing ensures that these advanced detectors continue to deliver the high level of fire safety they are designed for.

The 29 April 2025 was an important date for the fire industry in the UK and marked the publication of the new BS 5839-1:2025 Fire detection and fire alarm systems for buildings – Part 1: Design, installation, commissioning and maintenance of systems in non-domestic premises. Importantly, this new Code of Practice became effective immediately and officially replaced the 2017 version.

BS 5839-1 is important because it provides essential current practice to ensure fire alarm systems are reliable, compliant with regulations, and effective in real-world emergencies. Keeping up to date with BS5839-1 is crucial for anyone involved in fire safety, as it helps maintain high safety standards and supports legal compliance across the industry.

Anyone familiar with previous BS 5839-1:2017 clause numbering will need to get used to a new clause numbering in BS 5839-1:2025. In many cases the content has stayed the same, but it will be in a different place. For example, the functional testing of multi-sensor detectors is now covered in clause 43.3.13

Importantly, a wording change was made in clause 43.3.13. In c) it previously said “… Where the detection system design allows simultaneous stimuli and individual sensor responses to be verified either individually or collectively, the individual sensors may be physically tested together…”. The wording here has changed from ‘may’ to ‘should’.

In full: “43.3.13 Multi‑sensor detectors should be operated by a method that determines whether products of combustion in the vicinity of the detector can reach the sensors and that a fire alarm signal can be produced as appropriate. The following specific actions should be undertaken.

a) The manufacturer’s guidance on the manner in which the detector can be functionally tested effectively should be followed.

b) Multi‑sensor detectors should be physically tested by a method that determines whether

products of combustion in the vicinity of the detector can reach the sensors and whether the

appropriate response is confirmed at the CIE.

NOTE 1 Suitable test methods for each type of sensor are as described in this subclause, e.g. for heat sensors, see 43.3.6.

c) Where the detection system design allows simultaneous stimuli and individual sensor responses to be verified either individually or collectively, the individual sensors should be physically tested together. Where the system does not allow for this, each sensor on which a fire detection decision depends (e.g. smoke, heat, carbon monoxide) should be physically tested individually.

d) Where a system includes a time‑related configuration of detection, a sensor should not be

excluded from being tested as a result of the time‑dependent mode.

e) On completion of tests, the system should be returned to its normal configuration.

NOTE 2 Information regarding the configuration of multi‑sensor detectors and selection of types of detectors suitable for the application is given in Annex D, Figure D.1.

NOTE 3 Further information is given in the FIA guidance note Functional testing of point type multisensory detectors [19].”

This subtle change of wording has made a big impact. The ability to perform combined testing, that is where multiple sensing elements (such as smoke and heat) are tested simultaneously, depends on whether the fire alarm control panel can individually identify activations from each sensor channel. When supported, combined testing significantly improves efficiency through reduces maintenance time and costs. This is where all-in-one test devices like Testifire and XTR2 become essential. These are currently the only testers devices capable of performing genuine combination tests for multi-sensor detectors, making them perfectly aligned with the updated expectations of BS 5839-1:2025.

There is another important new wording in BS5839-1:2025 relevant to multi-sensor detectors and this is clause 43.2.10:

“43.2.10 All controls and visual indicators at the CIE should be checked for correct operation, and any timeclock should be checked and adjusted appropriately.

NOTE The correct time is particularly important where a time‑related filtering measure is adopted.”

Multi-sensor detectors offer the flexibility to operate in different sensing modes depending on the time of day or night. However, this functionality is only effective when the system’s internal timeclock on the fire panel is accurately set. An incorrect time setting can compromise the detector’s performance, potentially leading to safety risks.

For this reason, maintaining an accurate CIE timeclock is not just a best practice—it’s a critical requirement. This essential detail has now been formally recognized in the latest code of practice, reinforcing the importance of precise time configuration in time-dependent detection systems.

Finally, when it comes to the testing of detectors, people sometimes simply focus on the functional testing aspect. It is easy to forget that the visual inspection and the examination of detectors on-site are part of the testing protocol and play an important role. The numbering in

BS5839-1:2025 has changed and the visual inspection and the examination of automatic fire detectors are now covered in clauses 43.2.3 and 43.3.3 respectively.

“43.2.3 A visual inspection should be made to check whether structural or occupancy changes have affected the conformity of the system to this part of BS5839-1 for the sitting of manual call points, automatic fire detectors and fire alarm devices …”

“43.3.3 All automatic fire detectors (including those which are concealed or relatively inaccessible) should be examined, as far as possible, to verify that they have not been damaged, painted, or otherwise adversely affected.”

Similarly, part of this testing protocol for detectors is the LED check by the fire service engineer when physically on location and this is now covered in clause 43.3.4

“43.3.4 The correct operation of all readily visible integral and/or remote visual fire indicators should be checked. It should be verified that visual fire indicators are not obstructed from view by changes in their environment or contaminates such as paint …”

In summary, testing fire detectors involves more than just the functional test. A comprehensive approach includes three critical steps, each of which must be carried out at the detector itself:

• STEP 1 Visual Inspection & Detector Check

• STEP 2 Functional Testing

• STEP 3 LED Indicator Check

The rise of multi-sensor detectors and how to test them in BS5839-1

BS5839-1 & Functional Testing of Multi-sensor Detectors

BS5839-1 & CIE Timeclock

BS5839-1 & A Three-Step Approach for Testing Detectors

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