Magnetic Door Holders and Retainers on Fire Alarm Systems
Held-open fire doors are everywhere — they make buildings easier to move through and more accessible — but a fire door only does its job when it is shut. Magnetic door holders square that circle: they let a fire door stand open day to day, then release it to close the instant the fire alarm activates. Because they sit at the junction of the fire alarm system and passive fire protection, engineers need to understand how they work and, above all, how to confirm they release and close as intended. This guide covers both.
The essential point: a magnetic door holder keeps a fire door open only while the system is healthy, and releases it so the door closes on alarm — and usually on fault or power loss too.
Who this is for
This is for fire alarm engineers who install and service door holders, and for responsible persons who need to understand why held-open doors must release. The experience level assumed is competent engineer or an informed duty-holder. It explains the principle and the checks; the specific wiring, devices and which doors release on which events come from the system design, the cause and effect and the manufacturer's documentation.
What door holders do
A magnetic door holder, or retainer, holds a fire door open with an electromagnet and releases it automatically when the fire alarm activates, allowing the door to close. This gives the everyday benefits of an open door — easier movement, accessibility, airflow — without permanently defeating the door's fire and smoke resistance. The hold-open is entirely dependent on the fire alarm system: the door is held only while the system is quiescent and healthy, and the moment an alarm is raised the magnet releases and the door swings shut on its closer. In effect the holder lets the building have an open door until the one moment it must be closed.
Fail safe by design
The guiding principle behind door holders is fail safe. A fire door held open by a device that could fail with the door still open would be a hazard, so holders are arranged to release the door on loss of power and on a fault, not only on a fire signal. That way any failure — a power cut, a wiring fault, a system problem — results in the door closing, which is the safe state. This is why a held-open door dropping shut during a power interruption is the system behaving correctly, not a fault. The fail-safe arrangement is fundamental to using hold-open devices on fire doors at all.
How they connect and release
Door holders are operated by the fire alarm system, commonly through an output or interface so that an alarm condition removes power from the magnet and lets the door close. Which activations release which doors is a design decision recorded in the cause and effect — in some strategies all held-open doors release on any alarm, in others releases are zoned to match the evacuation plan. The wiring is arranged so the fail-safe behaviour holds, and the whole arrangement is designed and documented so it can be tested. As with any integration, the door holders only do the right thing if the cause and effect is correct and kept current.
What to check on service
On service, door holders are checked by proving the whole function, not just the magnet. Activate the fire alarm and confirm each held-open door releases and closes fully into its frame; confirm it also releases on power failure as intended; and check the door swing is clear and the closer brings the door properly shut. From field experience, the common findings are doors that release but do not close fully — a tired closer, a dropped hinge, an obstruction, a carpet catching — and doors that do not release at all. Either defeats the fire door, so both are worth chasing. This sits within the general duty to maintain appropriate fire precautions under the Regulatory Reform (Fire Safety) Order 2005: a held-open door is only acceptable if it reliably becomes a closed fire door when it matters.
When not to rely on this alone
When not to use this article: do not use it to wire or configure door holders for a specific installation. That requires the system design, the cause and effect, the current BS 5839-1 and the manufacturer's documentation, applied by a competent person. This guide explains the principle and the checks.
Professional disclaimer
This is an educational resource for competent engineers and informed duty-holders. It does not replace the current British Standards, manufacturer documentation or professional judgement. Confirm door-holder design, wiring and testing against the manufacturer's data and the current BS 5839-1.
Related reading
Read this with cause and effect in fire alarm systems, interfaces and I/O modules and testing and maintenance.