Interlinked means that when one alarm in the property detects smoke or heat, every alarm sounds, not just the one nearest the fire. That is the whole point of it: a fire starting in a downstairs kitchen still wakes someone asleep on the top floor. It says nothing about how the alarms talk to each other, and that part is where people get caught out buying or spec-ing a system.
Radio-interlinked or hard-wired
Hard-wired alarms are linked by a dedicated interconnect cable run between each unit, usually laid in at first-fix stage alongside the mains feed. It is the more reliable method because there is no signal to drop, but it means lifting floorboards or chasing walls if you are retrofitting into a property that already has its ceilings closed up.
Radio-interlinked alarms talk to each other wirelessly instead, each one still wired to the mains individually but broadcasting to the rest of the group rather than being cabled to them. Aico is one of the makes we fit most often for this — their RadioLINK range is a common way to bring an older property up to an interlinked standard without opening up the ceilings to do it. The trade-off is a battery back-up in every unit and, occasionally, a signal that needs a repeater in a larger or oddly shaped property.
Grade and category, in plain terms
A spec sheet or a quote for alarm work will often describe a system by a grade and a category rather than just saying "interlinked". Broadly, the grade describes how the alarms are powered and backed up — running from mains with a fitted battery back-up, or from battery alone — and whether the interlink is wired or radio. The category describes how much of the property is covered, from the minimum needed to protect the escape route through to alarms in most of the rooms where a fire could realistically start.
The exact letter your property needs depends on the type of building, who occupies it and, for a let property, the licence or tenancy conditions that apply. Do not assume from a general guide which grade and category applies to you — ask whoever is issuing the certificate or licence to state it plainly, and have it written on the paperwork rather than taken on trust.
What this means for a rented property
We cover the legal minimum for private rentals, and what changed in 2022, in a separate article. What is worth adding here is why interlinked matters more in a let property than an owner-occupied one: a landlord cannot rely on a tenant noticing a chirping alarm and doing anything about it before they move out, and an alarm that only sounds in the room where the fire started is a poor match for a property where people sleep behind closed doors on different floors.
HMOs in particular tend to be asked for more than the domestic minimum, often specified through the licence itself rather than general legislation. Again, that is a question for the licensing team or the certificate you are working towards, not something to assume from a blog post.
We fit and commission both hard-wired and radio-interlinked smoke and heat alarm systems, for homeowners and for landlords bringing a let property or an HMO up to standard in one visit.
If you are unsure, it is always cheaper to ask than to guess. Give us a call and we will tell you straight.