Every smoke detector is a compromise between responding early and responding to the wrong thing. The types differ in where they sit on that line, and choosing between them is a question about the room rather than about the technology. A detector that suits a hotel corridor is a poor choice for a loading bay.
Optical and ionisation
Optical detectors sense light scattered by smoke particles, and respond well to the larger particles of a smouldering fire, which is the fire that fills a house with smoke while people sleep. Ionisation detectors respond faster to the small particles of a fast flaming fire. Optical is the general purpose choice today, and ionisation has become less common in new domestic installations.
Multi sensor fire alarm heads
A multi-sensor combines optical smoke detection with heat sensing, and sometimes carbon monoxide sensing, in one head, using the combination to distinguish a real fire from steam, dust or cooking. They cost more and they are the sensible default in spaces with a history of unwanted alarms. They are not a licence to site a detector badly: a multi-sensor over a kettle will still be triggered.
Beam and aspirating
Optical beam detectors project a beam across a large open volume and detect the obscuration smoke causes, which suits atria, warehouses and sports halls where ceiling mounted point detectors would be unreachable and slow. Aspirating systems draw air through a pipe network to a very sensitive central sensor, and are used where the earliest possible detection matters or where the ceiling is genuinely inaccessible.
Choosing per room, not per building
The mark of a good design is a device schedule that names the type for each space and the reason. Corridors and offices take optical. Kitchens and plant rooms take heat. Areas with steam, dust or vehicle movement take multi-sensor. Tall open volumes take beam. A schedule with one type throughout is either a very simple building or a design nobody did.
Questions people ask about smoke detector types
Which smoke detector type is best?
There is no single best type. Optical suits most general spaces, heat suits kitchens and plant rooms, multi-sensor suits areas prone to false alarms, and beam or aspirating suit large open volumes.
Are multi-sensor detectors worth the extra cost?
In spaces with a record of unwanted alarms, usually yes, because the alternative cost is repeated callouts and eventually somebody disabling the device. In a quiet office they add little.
Should I still use ionisation detectors?
They respond well to fast flaming fires, but optical has become the general purpose choice and ionisation is less common in new domestic work. Follow the device schedule your designer produced rather than swapping types on site.
Do smoke detectors uk homes use differ from commercial heads?
The sensing is the same physics and the packaging is not. A domestic alarm is a self contained unit with its own sounder and often its own battery, made to be fitted by an electrician or by the householder. A commercial head is a detector only: it reports to a panel, which decides what sounds and where, and it is chosen from a device schedule alongside the rest of the system. Fitting domestic alarms in a building that needs a panel gives you noise in one room instead of a warning everywhere.
What do linked smoke detectors add over standalone ones?
The one thing that matters in a house, which is that a fire starting downstairs wakes somebody upstairs. A standalone alarm sounds where it is, and a closed door and a floor between is enough to make it useless. Interlinking, by cable or by radio, makes every alarm sound when any one of them detects. It is worth more than the number of alarms or the sensor type in almost every domestic case.
What is a vesda smoke detector, and where is aspirating detection used?
VESDA is a trade name, not a category. The category is aspirating detection: a pump draws air continuously through a pipe network into a central detector, so the sampling points are holes in a pipe rather than heads on a ceiling. It is used where point detection cannot work or cannot be reached, which means high atria, cold stores, plant and equipment cabinets, historic interiors where a visible head is unacceptable, and anywhere very early warning is worth paying for.