Kidde vs First Alert vs Google Nest: 12 Combination Smoke and CO Alarms Scored Out of 100

What each alarm does well, and what holds it back

Every alarm from ninth place up cleared the gate on the strength of Canadian documentation, and each one carries a 10-year limited warranty or a 10-year end-of-life design. The differences are in how they're powered, whom they can talk to and what they cost you per year.

9. Kidde 30CUDR-VCA: friendly and familiar, but you'll be changing batteries

This is the classic grab-and-go combo, with two AA batteries, voice alerts in English and French, Kidde's Hush button and a 10-year end-of-life reminder. At $84.97 at Home Depot Canada and $84.99 at Canadian Tire on capture day, it's reasonably priced. But it can't be interconnected, and AA batteries mean recurring changes and the dreaded 3 a.m. low-battery chirp. It suits a cottage bunkie or a single-storey rental where one standalone alarm is all you need.

8. First Alert SMCO210A: the lowest price per year in the field

At $64.99 at Canadian Tire, or $6.50 per year over its 10-year sealed battery life, this slim First Alert earned the top value score. First Alert Canada lists it to CAN/ULC-S531 and CSA 6.19. It's quiet and simple, with a single test-and-silence button and no voice. It also can't be interconnected, which is what keeps it in eighth place. If you live in a small, single-level home and want a sealed alarm you can forget about for a decade, it's a lovely fit.

7. Kidde 30CUD10-VCA: sealed, talkative and standalone

This Kidde pairs a sealed 10-year battery with voice alerts, Hush and a 24-hour alarm memory that tells you afterwards whether it detected smoke or CO while you were out. Kidde's own Canadian user guide for this family is refreshingly blunt: "This unit is not designed for interconnection." At $99.97 at Home Depot Canada, it's a good bedroom-hallway unit for homes without a hardwired loop, but it can't join one later.

6. First Alert SC5 battery: the smart bridge for Nest owners

The battery SC5 is Google's named replacement for Nest Protect, and its Canadian model (SMCO600NV-A) is listed to both Canadian standards. It speaks, it sends alerts to the First Alert app, it lets you check the peak CO level after an event, and it links wirelessly with other SC5 units and existing Nest Protects through the Google Home app. Two details pulled its score down. First, at $169.99 it works out to $17.00 per year. Second, First Alert's Canadian manual for the SC5 says it runs on six replaceable CR123A lithium batteries rather than a sealed cell, even though one First Alert Canada product page describes the battery as non-replaceable. We went with the manual.

5. Kidde hardwired smart combo: smart alerts for an existing Kidde loop

Home Depot Canada sells this app-enabled Kidde as SKU 21033406 for $114.00, and its listing names ULC S531 and CSA 6.19-17. It's designed to drop into an existing Kidde hardwired circuit, so one smart unit can send phone notifications for the whole interconnected system. That's a clever, affordable way to bring an older Kidde house online. It runs on AA backup batteries, though, and the listing doesn't print Kidde's own model number, so match the box to SKU 21033406 if this is the one you want.

4. First Alert SC5 hardwired: the wired Nest Protect replacement

The hardwired SC5 comes with a quick-connect adapter that plugs into an old Nest Protect harness, plus voice alerts, app notifications and an end-of-life notice in the app as well as on the alarm. First Alert Canada lists it to both Canadian standards. It ranks fourth rather than higher because its published interconnect list is short (other SC5 units, a First Alert CO alarm and Nest Protect) and because $169.99 is a lot of money per ceiling.

3. First Alert SC2-W10A: the sturdy First Alert workhorse

If your house is already wired with First Alert or BRK alarms, this is the one to look at first. It's hardwired with a sealed 10-year backup battery, it interconnects with most First Alert and BRK hardwired alarms, and the Canadian Tire listing notes a standardized mounting bracket and trim ring meant for replacement jobs. At $94.99, or $9.50 a year, it's very fair value. The only thing it gives up is voice: the manufacturer lists a horn tone and reminder chirps rather than spoken alerts.

2. Kidde 30CUAR-VCA: hardwired and interconnected at a sale price

Kidde's hardwired DETECT combo with AA backup carries the same voice alerts, Hush button and Kidde interconnect as our top pick. On October 1, Canadian Tire had it on sale at $69.99, while Home Depot Canada listed it at $99.97. At the sale price it works out to $7.00 per year, the lowest price per year of any interconnected alarm here. It loses out on power because AA backup batteries still need changing, but for a Kidde household on a budget it's a very happy compromise.

1. Kidde 30CUA10-VCA: the one that does the most for the longest

Our top score goes to the hardwired Kidde with a sealed 10-year backup battery. Kidde's Canadian user guide lists CAN/ULC-S531 and CSA 6.19, and the alarm interconnects with up to 24 Kidde devices. It speaks in English or French, offers an 8-to-10-minute Hush for burnt toast and keeps a 24-hour memory of what it detected. Ten years after power-up, it tells you out loud to "Replace Alarm." Canadian Tire listed it at $104.99 and Home Depot Canada at $109.00 on the same day, which works out to about $10.50 per year for a decade of no battery changes. Both retailers list it under the same Kidde number, 21032774, so that's the number to look for.

Why your next alarm is often chosen by your last one

Here's the quiet truth that the scores only hint at. Interconnected alarms only talk to their own family. Kidde's data sheet for its hardwired combo says it "is not designed to be interconnected with other manufacturer's products, unless otherwise specified." First Alert's hardwired SC2-W10A links with First Alert and BRK alarms. And the smart SC5 family links only with other SC5 units, one First Alert CO alarm and Google's Nest Protect.

In practice, that means the first question to ask yourself in the aisle isn't which alarm scored highest. It's which brand is already wired into your ceiling. If you have a Kidde loop, mixing in a First Alert alarm can leave that unit sounding on its own while the rest of the house stays silent. If you're starting fresh, or replacing every alarm at once because they've all reached their 10-year date, you're free to choose a family. In that case, pick one you can live with for the next decade.

It also helps to count how many alarms you actually need. Ontario's rules changed on January 1, 2026: as Ontario's Technical Standards and Safety Authority explains, existing homes with a fuel-burning appliance, a fireplace or an attached garage now need a CO alarm next to each sleeping area and on every storey, including storeys without bedrooms. For many Ontario households, that's three or four combos rather than one, and that's exactly when interconnect and price per year start to matter.

For a room-by-room walk through the new Ontario rules, see our guide to Ontario's new CO alarm requirements for 2026.

Three checks that take less than a minute in the store

Once you've chosen a family and a model, a few small habits make sure the alarm you carry home is the one you meant to buy:

• Find the Canadian mark. Look for CSA, cUL, ULC or cETL on the packaging, and for a CO-capable unit, check that CSA 6.19 is named. If you can only find UL 217 and UL 2034, keep looking.
• Read the date code. Kidde's guidance counts its 10-year replacement recommendation from the date code on the back of the alarm, while the built-in end-of-life timer counts from the day you power it up. An alarm that sat in a warehouse for two years can reach its 10-year mark long before it starts chirping, so pick the freshest date on the shelf.
• Match the model to the scorecard. Retailers often list their own SKU rather than the maker's model number. The Kidde at the top of our list appears as 21032774 at both Canadian Tire and Home Depot Canada.

Placement follows the same pattern across the country, with local twists. The Ontario Building Code's smoke alarm article calls for at least one smoke alarm on every storey including the basement, one in each bedroom and one in the hallway between the bedrooms and the rest of the floor. For CO, British Columbia's building code places alarms inside each bedroom or within 5 m of each bedroom door where a fuel-burning appliance is present. A combination unit in the hallway outside the bedrooms covers both jobs neatly, while bedrooms themselves can take smoke-only alarms from the same brand family.

If you'd like more help with spots like hallways, basements and the area near the furnace, our hub on CO and smoke detector placement under Canadian safety standards walks through each room.