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The best carbon monoxide detectors are cheap insurance against a gas you can’t see, smell or taste, and heating season is when furnaces, water heaters, fireplaces and space heaters run hardest. We compared specs, expert testing and owner reviews to pick nine CO alarms for every setup: simple plug-ins with a digital readout, sealed-battery units, hardwired voice alarms and smart models that ping your phone.
Part of our Home Comfort, Backup Power & Tool Guides.
Quick picks
Price ranges: $ under $30, $$ $30-$60, $$$ $60-$100, $$$$ $100+ (per alarm or pack as sold).
| Product | Best for | Price range | |
|---|---|---|---|
| First Alert SC5 Smart Smoke & CO Alarm | Best smart alarm overall | $$$$ | See price |
| Kidde Nighthawk KN-COEG-3 | Best plug-in with display | $$ | See price |
| First Alert CO615 | Best value plug-in | $$ | See price |
| Kidde Smart Carbon Monoxide Detector (COPDW) | Best budget Wi-Fi CO alarm | $$ | See price |
| X-Sense Carbon Monoxide Detector with Digital Display | Best sealed-battery digital | $$ | See price |
| Kidde Battery-Operated CO Detector | Best budget pick | $ | See price |
| First Alert SCO5CN Smoke & CO Alarm | Best battery combo | $$ | See price |
| First Alert SC7010BV Smoke & CO Alarm | Best hardwired with voice | $$$ | See price |
| First Alert Z-Wave Plus Smoke & CO Alarm | Best for Ring alarm owners | $$$ | See price |
1. First Alert SC5 Smart Smoke & CO Alarm: Best Smart Alarm Overall
With Google’s Nest Protect discontinued, First Alert’s SC5 is the smart smoke and CO alarm most experts now point to. It pairs a photoelectric smoke sensor with an electrochemical CO sensor, talks to the Google Home app over Wi-Fi, and links wirelessly with other compatible First Alert alarms so a CO alert in the basement sounds upstairs too. It can also use existing Nest Protect mounting hardware, which makes it an easy swap. There’s no subscription, though you also don’t get professional monitoring.
Key specs
- Type: combination smoke and CO alarm
- Power: battery or hardwired with battery backup versions
- Sensors: photoelectric smoke, electrochemical CO
- Smart features: Wi-Fi, Google Home app alerts, voice alerts, wireless interconnect
- Siren: 85 dB
👍 Pros
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👎 Cons
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What owners say: Owners like the phone notifications and how easily it replaced old Nest units; the most common gripe is being tied to Google’s ecosystem.
2. Kidde Nighthawk KN-COEG-3: Best Plug-In With Display
The Nighthawk has topped plug-in CO lists for years because it does the basics well: it plugs into an outlet, keeps running on a 9V backup battery during outages, and shows a live CO reading that refreshes every 15 seconds. A peak-level button shows the highest reading since the last reset, which is useful if you suspect a low-level leak overnight. It also senses explosive gases such as natural gas and propane, and a 6-foot cord adapter lets you mount it higher on a wall.
Key specs
- Type: CO plus explosive gas alarm
- Power: plug-in with 9V battery backup
- Display: digital, updates every 15 seconds
- Peak-level memory: yes
- Interconnect: no
👍 Pros
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👎 Cons
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What owners say: Reviewers value the readout and the extra gas sensing for homes with gas appliances, while some find it chunky enough to block the second outlet.
3. First Alert CO615: Best Value Plug-In
The CO615 gives you most of what the Nighthawk offers at a lower price. It plugs in, falls back to two AA batteries in an outage, and has a digital display with a peak-level button. A hush button quiets nuisance alarms and an end-of-life chirp tells you when the sensor is due for replacement. If you just want a reliable CO-only alarm with a readout for a bedroom hallway, this is a sensible default.
Key specs
- Type: CO only
- Power: plug-in with 2 AA battery backup
- Display: digital with peak level
- Siren: 85 dB
- Extras: hush button, end-of-life warning
👍 Pros
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👎 Cons
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What owners say: Owners describe it as simple and dependable; the main complaints are about the wall-mount bracket rather than the alarm itself.
4. Kidde Smart Carbon Monoxide Detector (COPDW): Best Budget Wi-Fi CO Alarm
If you want phone alerts without replacing your smoke alarms, Kidde’s Wi-Fi CO detector is one of the cheapest ways to get them. It shows a live ppm reading, keeps a peak-level memory and sends alerts through the Kidde app, and it can report status to Alexa and Google Home. It’s CO-only and doesn’t interconnect with other alarms, and it needs a 2.4 GHz network, so check your router before buying.
Key specs
- Type: CO only
- Power: plug-in with battery backup
- Connectivity: 2.4 GHz Wi-Fi, Kidde app, Alexa and Google Home status
- Display: live ppm with peak memory
- Siren: 85 dB
👍 Pros
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👎 Cons
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What owners say: Buyers like getting app alerts for the price of a basic alarm; setup on mixed-band routers is the most common frustration.
5. X-Sense Carbon Monoxide Detector with Digital Display: Best Sealed-Battery Digital
X-Sense’s CO alarm runs on a built-in battery rated for up to 10 years, so you never swap batteries and can mount it anywhere, not just near an outlet. An LCD shows the CO level, and a green, yellow and red LED gives an at-a-glance status. It often comes in multipacks, which makes covering every bedroom and level affordable.
Key specs
- Type: CO only
- Power: built-in battery, up to 10-year life
- Display: LCD ppm readout
- Status: three-color LED
- Often sold in multipacks
👍 Pros
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👎 Cons
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What owners say: Owners like the readout and the set-and-forget battery; a few wish it remembered peak readings.
6. Kidde Battery-Operated CO Detector: Best Budget Pick
For a guest room, an RV or a rental, Kidde’s basic battery CO alarm is about as simple and inexpensive as a trustworthy alarm gets. It runs on two AA batteries, sounds an 85 dB alarm, has a test button and uses red and green lights to show status, plus a low-battery signal. There’s no display or smart features, but it’s small enough to put almost anywhere.
Key specs
- Type: CO only
- Power: 2 AA batteries
- Siren: 85 dB
- Indicators: red and green LEDs, low-battery warning
👍 Pros
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👎 Cons
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What owners say: Buyers call it a no-fuss way to add coverage; those who want to see actual readings usually step up to a display model.
7. First Alert SCO5CN Smoke & CO Alarm: Best Battery Combo
If you’d rather have one device per ceiling than two, the SCO5CN combines a photoelectric smoke sensor and an electrochemical CO sensor in one battery-powered alarm. No wiring is needed, and locking pins on the battery drawer discourage anyone from “borrowing” the batteries. It’s a solid upgrade for older homes that only have smoke alarms.
Key specs
- Type: combination smoke and CO alarm
- Power: battery only
- Sensors: photoelectric smoke, electrochemical CO
- Siren: 85 dB
👍 Pros
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👎 Cons
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What owners say: Owners appreciate replacing two devices with one; the battery drawer design is the recurring complaint.
8. First Alert SC7010BV Smoke & CO Alarm: Best Hardwired With Voice
Homes with existing hardwired smoke alarms should stick with hardwired replacements so every alarm sounds together. The SC7010BV interconnects with up to 18 compatible devices when hardwired, has battery backup, and speaks the hazard type and one of 11 programmable locations, so you hear “carbon monoxide in basement” instead of a generic beep. It’s often sold in multipacks for whole-house replacements.
Key specs
- Type: combination smoke and CO alarm
- Power: hardwired with battery backup
- Interconnect: up to 18 devices when hardwired
- Voice alerts with 11 preset locations
👍 Pros
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👎 Cons
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What owners say: Owners like the spoken location alerts and easy swap onto existing harnesses, though some find the voice hard to make out.
9. First Alert Z-Wave Plus Smoke & CO Alarm: Best for Ring Alarm Owners
If you already have a Ring Alarm or SmartThings hub, this Z-Wave Plus combo alarm reports smoke and CO events straight into that system. It runs on two AA batteries and is listed to UL 217 for smoke and UL 2034 for CO. It doesn’t work with Google Home or Apple HomeKit, and you can’t silence it from the app.
Key specs
- Type: combination smoke and CO alarm
- Power: 2 AA batteries (included)
- Connectivity: Z-Wave Plus; works with Ring and SmartThings
- Listings: UL 217 (smoke), UL 2034 (CO)
👍 Pros
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👎 Cons
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What owners say: Ring users like seeing alarm events alongside their security system; others note it needs a Z-Wave hub to be “smart” at all.
How to choose the best carbon monoxide detector
- Look for UL 2034 and an electrochemical sensor. UL 2034 is the US standard for residential CO alarms, and experts favor electrochemical sensors for accuracy.
- Match power to the spot. Plug-ins with battery backup are easy near outlets; sealed-battery units mount anywhere; hardwired alarms make sense if your home already has interconnected wiring.
- Decide on CO-only or combo. Combo smoke and CO alarms reduce clutter and are a good choice when you’re replacing old smoke alarms anyway. Keep CO-only units if your smoke alarms are new.
- Interconnect if you can. An alarm in the basement is only useful if you hear it from a bedroom. Wireless or hardwired interconnect makes every unit sound together.
- A display and peak memory help. A ppm readout shows low, lingering levels that may not trigger an alarm yet, and peak memory reveals what happened while you were asleep or away.
- Smart alerts are for when you’re away. App notifications matter most for vacation homes, rentals and anyone who travels.
- Plan for replacement. CO sensors wear out. Sources put typical lifespans between about 5 and 10 years; check the date on the back and the end-of-life signal.
Installer tip from our HVAC team: a CO alarm is a backup, not a substitute for maintenance. Have furnaces, boilers and gas water heaters checked by a qualified technician each year, keep flues and vents clear of snow and debris, and never run generators, grills or vehicles in an attached garage, even with the door open.
FAQ
Where should I put carbon monoxide detectors?
Safety agencies recommend at least one CO alarm on every level of the home, including the basement, and one outside each sleeping area; CPSC also suggests one inside each bedroom. Follow your alarm’s manual for exact height and distance from fuel-burning appliances, and avoid spots right next to fireplaces, in bathrooms or in dead-air corners.
How often should I replace a carbon monoxide detector?
Follow the manufacturer’s date on the unit, usually somewhere between 5 and 10 years. Test monthly, and replace batteries on the schedule in the manual unless the alarm has a sealed long-life battery.
Is a smoke detector the same as a CO detector?
No. A standard smoke alarm won’t detect carbon monoxide. You need a dedicated CO alarm or a combination smoke and CO alarm that is listed for both.
What should I do if my CO alarm goes off?
Get everyone, including pets, outside to fresh air right away, then call 911 or your gas utility from outside. Don’t go back in until responders say it’s safe, and have your fuel-burning appliances inspected before using them again.
Related guides
- The Best Space Heaters of 2026
- No Heat in Winter: How to Stay Warm When the Furnace Stops
- The Best Smart Thermostats of 2026
- Winter Storm and Power Outage Prep
- Home Comfort, Backup Power & Tool Guides
Sources
Security.org: The Best Carbon Monoxide Detectors of 2026; Reviewed: Best Smart Smoke and CO Detectors; Bob Vila: Best Carbon Monoxide Detectors; Popular Science: The Best Carbon Monoxide Detectors. Owner feedback is summarized in our own words from public reviews. Photos courtesy of Unsplash.