Testing a smoke alarm takes a few seconds and most people do the part that proves the least. The button on the front proves the sounder and the electronics behind it. It does not prove that the sensing chamber can still see smoke, which is the thing that actually saves the household, and that is why alarms carry a replacement date as well as a test button.
How to test smoke detectors: the test everybody knows
Press and hold the test button until the alarm sounds. On an interlinked set, every other alarm in the property should sound within a few seconds. Release the button and the alarms should silence themselves. If one alarm in an interlinked set stays quiet, the fault is in the link or in that unit, and testing from a different alarm in the set is the quickest way to work out which.
What the button does not prove
The test button runs a self check of the horn and the circuitry. On most domestic alarms it does not push smoke through the chamber, so an alarm whose sensor has drifted or clogged can pass its own test every week and fail on the night. That is the reason manufacturers state a service life, usually printed on the back beside the date of manufacture, and the reason replacement is scheduled rather than waiting for a failure.
When it beeps rather than sounds
A single chirp at intervals is usually a low battery or an end of life warning, and the two are easy to confuse. The manual tells you which pattern means which. An end of life alarm cannot be fixed with a battery, and an alarm that keeps chirping after a new battery is almost always telling you its life is up. Sealed ten year units have no user replaceable battery at all and are designed to be swapped whole.
How to do a fire alarm test in a workplace system
In a non-domestic building the equivalent routine is operating a manual call point with the test key, confirming the sounders are audible where people need to hear them, then resetting the panel and recording it. Detectors themselves are proved during the periodic service using test apparatus, not by pressing anything on the unit. Do not treat the panel's own lamp test as evidence that detection works.
Other questions people ask
How often should a smoke alarm test be done at home?
On a schedule you will actually keep. BS 5839-6 is the relevant standard for dwellings and the practical advice everywhere is regular, short tests plus replacement at the end of the stated service life.
Can I test a smoke alarm with real smoke?
Do not use a naked flame or a smouldering source. Aerosol test sprays exist and are what a professional uses on a detector head. For a domestic alarm the button plus replacing the unit on time is the regime the standards expect.
My alarm sounds on the test but not when I burn toast. Why?
That is exactly the failure the test button cannot see, and it means the sensing chamber is no longer working properly. Replace the alarm rather than trying to clean it back into service.
Is a smoke alarm tester worth using at home?
It closes the gap the button leaves. The button proves the sounder and the electronics; an aerosol tester puts something into the chamber and proves that the sensing element still responds, which is the half that degrades with age. It is what an engineer uses on a workplace system. At home it is worth it on alarms that are a few years old, and no substitute for replacing one that has reached its marked date.