Best smoke and CO combo in CO alarms
One sealed 10-year-battery alarm for smoke and CO, unaffected by outages, with no battery changes. Listed to UL 217 10th edition and UL 2034 (US model).
Our score: 8.2/10 out of 10Researched, not lab-tested
- Detects
- Smoke and carbon monoxide
- Power
- Sealed 10-year battery
- Canadian listing
- None stated (US model)
- Warranty
- 10 years
Is it right for you?
Pros
- Conforms to UL 217 (10th edition) and UL 2034, per First Alert
- Sealed 10-year battery: no battery swaps and no outage worries
- Photoelectric smoke sensor and electrochemical CO sensor
- 10-year limited warranty; end-of-life warning
Cons
- US model: no Canadian (CSA 6.19) listing stated
- Battery can't be replaced: the whole alarm goes after 10 years
- No display, so you can't see a low CO reading
- Not a substitute where code requires hardwired smoke alarms
- Best for
- US homes replacing old smoke alarms that want CO covered at the same time, on every level and in bedrooms, with no batteries to forget.
- Not for
- Canadian homes, homes whose code calls for hardwired alarms, and anyone wanting a CO number on a display.
Our verdict
A sealed 10-year battery is the reason this alarm suits outage-prone homes: it doesn’t depend on mains power at all, and there is no backup battery to forget. The SMCO210 detects smoke with a photoelectric sensor and CO with an electrochemical one, and First Alert lists it as conforming to UL 217 (10th edition) for smoke and UL 2034 for CO, the US standards. It has an end-of-life warning and a 10-year limited warranty.
For a US home replacing old battery smoke alarms, it covers both hazards in one device per room. The trade-offs: the battery can’t be replaced, so the whole alarm goes after ten years; there is no display for a CO reading; and where local code requires hardwired, interconnected smoke alarms it doesn’t fill that role. It is a US model, sold only with US listings on First Alert’s page, so we don’t recommend it for Canadian homes.
Setup and safety
If the CO alarm sounds, get everyone out at once, call 911 from outside and don’t go back in (Health Canada). An alarm doesn’t make an indoor generator safe: run generators outdoors only, at least 6 m (20 ft) from the house, exhaust pointed away from doors and windows (CPSC).
Where it goes. First Alert recommends combination alarms on every level and in every bedroom. Health Canada says the most important place for a CO alarm is the hallway outside sleeping areas, and CPSC asks for CO alarms on every level and outside sleeping areas, interconnected where possible (Health Canada).
Keeping it working. Press the test button regularly; CPSC suggests monthly. There is no battery to change, so when the end-of-life warning sounds, or ten years are up, replace the whole alarm.
In Canada. Health Canada asks buyers to choose CO alarms with a Canadian certification mark on both the alarm and its packaging, and to confirm this with online sellers. First Alert’s page for this model shows no Canadian listing. See the CO alarms we compare.
Specs
First Alert SMCO210 10-Year Battery Smoke and CO Alarm
Alarm
| Detects | Smoke and carbon monoxide |
|---|---|
| Power | Sealed 10-year battery |
| Sensor | Electrochemical (CO); photoelectric (smoke) |
| CO reading display | No |
| End-of-life warning | Yes |
Listing
| US listing | UL 2034; UL 217 10th ed. (smoke) |
|---|---|
| Canadian listing | None stated (US model) |
Other details
| Warranty | 10 years |
|---|
Maker’s figures, checked 3 Nov 2026.
SMCO210 questions
Does the SMCO210 work in a power outage?
Yes. It runs on its sealed 10-year battery all the time and never uses mains power, so an outage changes nothing. That matters because outages are when generators, fuel heaters and hard-working furnaces raise the risk of carbon monoxide.
Can I replace the battery?
No. The battery is sealed in for the alarm’s life. When the end-of-life warning sounds, or ten years after you fit it, replace the whole alarm. The limited warranty also runs ten years.
Do I still need separate smoke alarms?
This one detects both smoke and CO, so it can do both jobs where it is fitted. A plain smoke alarm doesn’t detect CO, Health Canada notes. If your home’s code calls for hardwired, interconnected smoke alarms, keep those, and check local rules before swapping.