Interlinking means that when one alarm detects a fire, every alarm in the property sounds. It matters because the point of detection is to wake or warn people who are not in the room where the fire started, and a single sounding unit two floors below an occupied bedroom does not do that. It is the single biggest improvement available in domestic fire detection.
What it achieves
A fire that starts in a kitchen at night is detected by the kitchen device, and the alarm sounds in the bedrooms. Without interlinking, the people who need the warning most are the least likely to get it, because they are furthest from the fire and behind a closed door. Every study of domestic fire deaths points at the gap between detection and warning.
Wired and radio interlinking
Mains powered alarms are interlinked by a dedicated interconnect conductor run between them, which is the traditional method and requires the cabling to be there. Radio interlinked alarms pair over a wireless link and are the practical route in an existing property, because they need no new cable between rooms. Both are acceptable where the product is designed for it, and mixing manufacturers generally does not work.
Where the law requires it
Scotland requires interlinked alarms in every home regardless of tenure, with a defined arrangement of smoke and heat alarms. In England the requirements for rented property are expressed differently and are about provision and repair rather than interlinking, and the building regulations require interlinked alarms in new and materially altered dwellings. The result is a patchwork, and a landlord operating across borders has to read both.
Mains, battery and the hybrid
Mains powered alarms with a battery backup are the standard for new work because they cannot be disabled by removing a battery. Sealed long life lithium battery alarms avoid the electrical work and are accepted in many retrofit situations. What matters more than the power source is that the units are interlinked and that they are in the right places.
Questions people ask about interlink fire alarm
Can an electric fire alarm be interlinked with a battery one?
Only where the manufacturer supports it, usually through a radio module. Mixing brands or technologies without that support produces units that do not talk to each other.
How many alarms does a house need?
It depends on the layout and the jurisdiction. The common pattern is one in the main living room, one in each circulation space on each storey, and a heat alarm in the kitchen.
Does interlinking need testing?
Yes. Pressing the test button on one unit should sound all of them, and that is the test worth doing rather than testing each unit alone.