A fire door alarm is a small device fitted to a door that sounds locally when the door is held open beyond a set time. It is not part of the fire alarm system and it does not close anything. It exists to tell somebody that a door is being propped, which is a management problem the building has probably already failed to solve by instruction.
What it does and does not do
It detects that the door is open, waits a set delay, and sounds a local alert. It does not release the door, does not signal the fire alarm panel, and does not contribute to the fire strategy. Treating it as a fire safety measure in an assessment would be an error; treating it as a way of finding out where the wedging happens is exactly right.
Where monitoring earns its place
On doors that are repeatedly found propped, on doors in areas with no passing supervision, and during a period when a building is trying to change behaviour. The data is the point: after a few weeks the pattern shows which doors are a genuine operational problem, and those are the doors that need a hold open device rather than another notice.
Monitored doors on the alarm system
A different product does report to the panel: door position monitoring on critical doors, used in some higher risk buildings so that the panel and any remote monitoring know whether compartmentation is intact. That is a designed system feature and belongs in the fire strategy, unlike the standalone alarm.
The limits
A local sounder nobody hears changes nothing, and in a building where propping is chronic the alarms are quickly disabled or their batteries left flat. The device buys information and a little friction. The fix for a door that genuinely needs to stand open is a release device, and the fix for a door nobody needs is often removing the reason it is used at all.
Questions people ask about fire door alarm
Is a fire door alarm a legal requirement?
No. It is a management aid. The legal requirement is that the door is closed when a fire occurs and that the measures are maintained.
Does it replace a hold open device?
No. It tells you the door is open; a release device lets the door be open legitimately and closes it on alarm. They answer different problems.
Should the alerts be recorded?
They are worth recording informally while a building is diagnosing where its propping happens, because that record is the business case for the release devices.