Hardwired Interconnected Smoke Alarm

How it works

A 120 V circuit powers the alarm and keeps a backup battery charged. A third conductor — the interconnect wire — carries a signal between units, so when one detects smoke it triggers every alarm on the loop. Newer systems achieve the same thing over a radio link instead of a wire.

What the market looks like

This is a two-brand market in North America. Kidde and First Alert (BRK) between them hold most of the shelf space, with a long tail of Universal, Ecoey and house brands. Prices run CAD $25 to $70 per unit. The real differentiators are sensor type, whether the unit is combination smoke/CO, and whether interconnection is wired or wireless — not brand. Every unit sold legitimately in Canada or the US is tested to UL 217 or CAN/ULC-S531, so the certification is a floor rather than a selling point.

Features that actually matter

Interconnect wiring

The third wire is the whole point. Codes in both countries require that when more than one alarm is needed, any one sounds all of them within the dwelling.

Battery backup

Required by code and the reason the hardwired failure rate is low. Power failure accounted for only 7% of alarm failures in NFPA's data.

Sensor type

Ionisation is faster on flaming fires, photoelectric on smouldering ones. Dual-sensor units exist and are what USFA recommends if you are not mixing types across the house.

UL 217 8th edition or later

The current standard adds smouldering and flaming polyurethane tests plus a cooking nuisance test. Worth checking, because when NIST tested 45 models against the new criteria, not one met all of them.

Wireless interconnect option

Listed wireless interconnection is accepted for retrofits in the US and in Ontario for houses with secondary suites. Elsewhere in Canada the code language still says wired — check before relying on it.

What it really costs

Up front

CAD $25-$70 per alarm. A typical two-storey house with basement needs five to eight.

Consumables

Backup batteries every year or two on units that have replaceable ones.

What else you'll need

Electrician time if the wiring is not there — commonly CAD $150-$400 per location, which is what makes retrofit uneconomic.

Over five years

Essentially the purchase price. The whole unit is replaced at ten years from manufacture regardless of condition.

Figures are typical street prices in Canadian and US dollars as of September 2026, gathered from public retail listings. They move with the season and with the exchange rate — treat them as a planning band, not a quote.

How it differs from the alternatives

Versus battery-only alarms

The gap is real and measurable: 93% operation versus 79%. Almost all of the difference is human — missing or dead batteries accounted for 71% of all alarm failures and 87% of battery-only failures.

Versus sealed ten-year units

Hardwired wins on reliability and interconnection; sealed units win overwhelmingly on retrofit cost. For an existing finished house, sealed is usually the right answer.

The ten-year rule

Alarms are replaced ten years from the date of manufacture printed on the back — not from when you installed them, and not when the battery dies. This applies to hardwired units too, and is the most commonly ignored rule in home fire safety.

If not this, then what

• Sealed ten-year lithium alarmsThe best retrofit. Removes the dominant failure mode without an electrician.
• Wireless-interconnected battery alarmsInterconnection without wiring. Accepted in US retrofits; check your provincial code in Canada.