Smoke & CO alarms
An interconnected system sounds every alarm in the house when one detects smoke. In a single-storey house at night that difference is measured in seconds.
What it involves
The difference between a house with alarms and a house with an alarm system is interconnection.
In an interconnected system, one alarm detecting smoke sounds every alarm in the house. A fire starting in a garage or a back bedroom is announced in the room where people are sleeping, rather than by a single unit nobody hears through a closed door. Standalone battery alarms cannot do this. In a single-storey house at night the difference is measured in seconds, and seconds is the whole margin.
Hard-wired units take power from a circuit and hold a battery for outages, so a dead battery does not silently leave the house unprotected and an outage does not either. The battery still needs replacing — the backup is a backup, not a substitute for maintenance.
Broadly: inside each sleeping room, immediately outside each sleeping area, and on every level including basements. Carbon monoxide alarms go outside sleeping areas and on each level where there is any fuel-burning appliance or an attached garage. Placement details matter more than people expect — too close to a kitchen or bathroom produces nuisance alarms, and a nuisance alarm is one that eventually gets disconnected.
Carbon monoxide is a colourless, odourless gas produced by anything burning fuel, and it is not detected by a smoke alarm. Combination units cover both; separate units are equally valid. What is not valid is assuming a smoke alarm gives any CO warning at all, because it gives none.
Where running interconnect wiring between existing alarm positions is impractical, wireless interconnection between hard-wired units achieves the same behaviour without opening ceilings. Which approach makes sense depends on what is already in place and what routes exist, so it is decided on site.
Check this yourself
No electrician needed for this part, and it is the thing most likely to be out of date in any given house.
Take a unit down and look at the back. There is a manufacture date printed on it. Smoke alarms are generally replaced around ten years from that date and CO alarms sooner, because the sensing elements degrade with time rather than with use — an alarm that has never once sounded is exactly as expired as one that has. A house that has changed hands in the last decade very often has alarms older than the current owner assumes, because nobody thinks to check.
Testing monthly with the test button and keeping the covers free of dust are the other two things worth doing, and both are genuinely homeowner jobs. Where it stops being one is the wiring: a hard-wired unit sits on a live circuit, and mismatched models on one interconnect loop routinely fail to talk to each other. If yours are past their date, replacing them as a set is the reliable move — and it is often combined with other small electrical work in a single visit.
Useful to include: how many levels and bedrooms, whether existing alarms are wired or battery-only, the manufacture date if you have checked, and whether there is a gas appliance, fireplace or attached garage.
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The units themselves, not just the batteries, are generally replaced about every ten years — the sensors degrade whether or not the alarm has ever sounded. Carbon monoxide alarms are typically shorter, often five to seven years, and many now end their life with a specific end-of-life signal. Every unit carries a manufacture date on the back, and reading it is the single most useful thing a homeowner can do here. An alarm past its date is decoration.
That is interconnection working as designed, and it is the feature rather than a fault. Most models indicate which unit originated the alarm — a different light pattern or a marker on the initiating unit — so the source can be found. If alarms are sounding with nothing present at all, that is a different problem: usually dust, insects, humidity, steam, or a unit at the end of its life.
Replacing the battery, testing monthly and vacuuming dust from the cover need no electrician at all, and are worth doing. Swapping a hard-wired unit means working on a live circuit at a ceiling connection, and mixed models on one interconnect loop frequently do not communicate — different manufacturers use incompatible signalling even where the connector looks identical. If the units are past ten years, replacing them as a set is both safer and more likely to actually work.
A fully electric house with no attached garage has no obvious CO source, so the case is weaker. Anything that burns fuel changes that: a gas furnace or water heater, a gas range, a fireplace, or an attached garage where a vehicle runs even briefly. Portable generators are the other one worth naming, because running one in a garage or near an open window is a recurring cause of poisoning after storms.
Usually. Where interconnect wiring cannot practically be run between positions, wireless interconnection between hard-wired units gives the same all-sound behaviour without opening ceilings. Where a house has no alarm circuit at all, one has to be provided, and how straightforward that is depends on attic and crawl space access — which in much of Lawton's single-storey housing is reasonable.
Tell us how many bedrooms and levels the house has and what is fitted now, and we will tell you what a working interconnected system takes.