Carbon Monoxide Detectors
The Best Carbon Monoxide Detectors
Every listed alarm has passed the same UL 2034 tests, so the differences that matter are power, display and whether the unit records a peak you were not there to see.
By Ryder M.Last reviewed
Buy the First Alert CO710 for most homes: a UL 2034 alarm with a backlit digital display and a sealed ten-year battery, which means it goes at the height and position the room needs rather than wherever the outlet is, and First Alert publishes that it stores a recent peak CO reading — the record that catches a slow leak from a cracked heat exchanger that never reaches the alarm threshold while anyone is watching. If you would rather have a live reading at outlet height with mains power behind it, the Kidde COPD is the plug-in to buy. One per level, within earshot of the bedrooms.
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What UL 2034 actually requires
This is the single most useful thing to understand before buying, and almost nobody explains it. UL 2034 is the standard for single- and multiple-station carbon monoxide alarms, and it specifies response times paired with concentrations:
At 70 ppm, the alarm must sound within 60 to 240 minutes. At 150 ppm, within 10 to 50 minutes. At 400 ppm, within 4 to 15 minutes. And — critically — the alarm must not sound below 30 ppm at all.
That last requirement is deliberate. It exists to prevent nuisance alarms, because low concentrations of CO occur in ordinary life and an alarm that fired at 15 ppm would be silenced within a week. CPSC's conformance testing work and the NFPA research foundation's review of alarm thresholds both work through the reasoning.
So a listed CO alarm is designed to prevent acute poisoning in a healthy adult. It is not designed to tell you the air is slightly bad, and for most households that is the right engineering. For some households it is not, and low-level monitors is the page for that.
A unit with a readout and a peak-level memory will at least tell you what happened above that floor while the house was empty, which is the most useful thing a domestic CO alarm does. CO detectors with a digital display covers which models record it and how low.
Renting changes the constraints rather than the hazard: best CO detectors for apartments covers alarms that need no drilling and no outlet, and why a peak-level memory is worth more to a tenant than to a homeowner.
If somebody in the household is a young child, an older adult or pregnant, it is worth reading the Kidde COBDL review as well — that alarm alerts in the 30-70 ppm band a standard UL 2034 alarm is permitted to ignore.
The UL 2034 response requirements
| Concentration | Alarm must sound within | What it means |
|---|---|---|
| Below 30 ppm | Must NOT alarm | Deliberate, to prevent nuisance alarms. This is why a live display often reads zero when there is genuinely something there. |
| 70 ppm | 60-240 minutes | A long window, because at this level the risk is cumulative rather than immediate. |
| 150 ppm | 10-50 minutes | Getting serious. Symptoms are likely before the alarm at the top of that window. |
| 400 ppm | 4-15 minutes | Dangerous. This is the fast-response case the standard is really built around. |
Requirements as specified in UL 2034 and summarized in CPSC's conformance report.
How we ranked these
We ran no tests. Every unit here is UL 2034 listed, which means it has already passed the response-time testing above — that is third-party evidence and it is more than we could generate.
So the scoring is about everything the listing does not decide. Listing and compliance is whether the unit is properly listed and how long the manufacturer states it lasts. Reading and display is whether it reports a number or just alarms. Peak-level memory is whether it records a concentration you were not present for, which is the difference between finding a slow leak and missing one. Power resilience is what happens in an outage — the hours when CO risk is highest. Placement freedom is whether the unit can go where the room needs it or only where an outlet is.
What is not in the list: price, which we report but never rank on, and star ratings, which we will not launder into a score. Brand is not in the list either, because the listing settles detection — but the two brands that own this category do differ on warranty, mounting and low-level alerting, which is the subject of Kidde vs First Alert CO detectors.
Quick picks
Scored against listing and compliance, reading and display, peak-level memory, power resilience and placement freedom. Tap a row for the full write-up. The price in each buy button is the live Amazon price at the last check, stamped with the date it was taken.
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  First Alert CO710 Sealed-Battery CO Alarm Sealed ten-year battery, a backlit digital display, and the one peak-reading claim still published in this category. Placement freedom is why it leads. | Most homes — the position the room needs, and a peak record | 8.7/ 10 | $44.49 · View on Amazon #ad how we are funded · price as of November 11, 2026 |
| 2 |  Kidde COPD Plug-In CO Alarm with Digital Display Kidde's current plug-in alarm: mains power with AA backup and a backlit display at outlet height. What it no longer has is a published peak memory. | A hallway outlet — a live reading at a height you can read | 7.8/ 10 | $43.97 · View on Amazon #ad how we are funded · price as of November 11, 2026 |
| 3 |  First Alert CO615 Plug-In CO Alarm with Battery Backup Outlet height puts the display where a human can see it without a stepladder. | A hallway you will actually read | 7.8/ 10 | $44.95 · View on Amazon #ad how we are funded · price as of November 11, 2026 |
| 4 |  Kidde KN-COPP-B-LPM Battery CO Alarm with Digital Display Battery only with a display and peak memory — the portable option. | Travel, cabins and rooms with no power | 8.1/ 10 | $27.97 · View on Amazon #ad how we are funded · price as of November 11, 2026 |
The four alarms in full
1. Most homes — the position the room needs, and a peak record
First Alert CO710 Sealed-Battery CO Alarm
Sealed ten-year battery, a backlit digital display, and the one peak-reading claim still published in this category. Placement freedom is why it leads.
- Listed to
- UL 2034
- Sensing / agent
- Electrochemical CO sensor
- Power / service life
- 10-year sealed battery
The argument for a sealed-battery unit is placement freedom, and in CO detection that matters more than it does for smoke alarms. Because carbon monoxide mixes with air rather than reliably rising, manufacturers' instructions vary on height — and a plug-in alarm has already made that decision for you by being at outlet height.
It also matters for hearing it. The requirement that actually saves lives is that the alarm wakes people, which means it needs to be where the bedrooms are rather than where the wiring is. A sealed unit goes on a bedroom wall or a landing ceiling without an extension lead.
On the peak reading. This is the feature worth understanding, because it is the one thing a domestic alarm does that nothing else does: it tells you what happened while you were out. A UL 2034 alarm is forbidden from sounding at low concentrations, which means an appliance producing a steady low level will never alarm — and that is exactly the signature of a cracked heat exchanger or a partially blocked flue. A stored peak reading gives you evidence of it. What we will not do is quote you a floor figure: First Alert publishes that it stores a recent peak in ppm, and it does not publish how low that record goes.
The trade is that a sealed unit is a ten-year consumable. That is the correct design for a device whose electrochemical sensor has a finite life anyway — replacing the sensor and the horn and the housing together is cleaner than pretending a fresh battery restores a decade-old cell. Lifespan and replacement covers the arithmetic.
What it does well
- 10-year sealed battery — no outlet needed and nothing to replace for a decade
- Backlit digital display showing the measured concentration and the room temperature
- **First Alert publishes that it stores a recent peak CO reading in parts per million**, which is the record that turns a hunch about an appliance into a service call
- Goes at whatever height and position the room actually needs, which matters more for CO than it does for smoke
- No low-battery chirp until the unit is genuinely at end of life
The downside
- At end of life the whole unit is replaced, by design
- No mains power, so nothing keeps it running if the sealed cell fails early
- **First Alert does not publish a peak-memory floor**, so there is no stated figure for the lowest concentration it will record — treat the peak reading as a record, not as a measurement instrument
- First Alert's own product page now marks the CO710 discontinued even though the retail listing is still in stock, so the line may not be restocked indefinitely
Do not buy this if: you want the cheapest possible per-unit cost and you have outlets everywhere. A plug-in unit with a replaceable backup battery is less expensive up front; the sealed unit wins over ten years and wins on placement.
- Sealed 10-year battery — nothing to change, and no low-battery chirp until it is genuinely done
- Digital display showing the measured concentration
- Placement is free: no outlet required, so it can sit at the height the room actually needs
- End of life means replacing the whole unit, by design
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2. A hallway outlet — a live reading at a height you can read
Kidde COPD Plug-In CO Alarm with Digital Display
Kidde's current plug-in alarm: mains power with AA backup and a backlit display at outlet height. What it no longer has is a published peak memory.
- Listed to
- UL 2034 5th edition; ETL listed
- Sensing / agent
- Electrochemical CO sensor
- Power / service life
- 120V AC with two AA backup batteries, included; 10-year limited warranty on the alarm
What this alarm is for. A plug-in CO alarm earns its place on one argument: mains power with a battery behind it, at a height a person can actually read. Power outages are exactly when households run generators and alternative heating, which is when CO risk peaks, and an alarm on house power with AA backup is awake through all of it.
What changed, and why we are telling you. This slot used to hold Kidde's Nighthawk KN-COPP-3, and the reason it led this roundup was Peak Level Memory — a stored record of the highest concentration the unit had seen. That alarm is no longer sold, and no alarm in Kidde's current CO range publishes a peak memory at all. We checked the whole line. So the recommendation moved: the peak record now sits with the First Alert CO710, and the Kidde plug-in is here for the live reading and the mains power.
On the display: Kidde publishes that it shows the level of CO being sensed and does not publish a range or a refresh rate, so we are not going to quote you one. What is worth knowing is the standard behind it — a UL 2034 alarm is not required to display anything below 30 ppm, so a readout of zero is not proof of zero. That is the standard's design, and it is exactly why low-level monitors exist as a separate product class.
Do not plug it in directly above a furnace or water heater. Fuel-burning appliances produce a brief spike on start-up, and an alarm in the plume will nuisance-trip. Where to install CO detectors has the positions.
What it does well
- **Listed to UL 2034 5th edition and ETL listed** — the current edition of the standard, which is the most useful thing on the box
- Backlit display shows the level of CO the alarm is sensing, at outlet height where you can read and test it without a stepladder
- **Mains powered with two AA backup batteries included**, so it keeps monitoring through the outage that brings the generator out — which is when household CO risk peaks
- Rotating plug fits a vertical or a horizontal outlet, with published power-surge immunity
- Kidde publishes no nighttime low-battery chirps, plus a 10-year limited warranty on the alarm
The downside
- **No published peak-level memory.** The Kidde plug-in used to be the peak-memory alarm in this category and the current model is not — Kidde publishes no peak record for the COPD, and nor does any other current Kidde CO alarm. If a stored peak is what you want, the CO710 above is the pick
- Tied to an outlet position, so it cannot go wherever the room needs it — and the outlet is rarely where the furnace is
- The backup cells are replaceable AAs, so the annual check is real even though Kidde says it will not chirp at you overnight
- No published ppm range or refresh interval for the display, so treat the reading as an indication rather than an instrument
Do not buy this if: the position you need has no outlet, or you want a stored peak reading. For the first, buy the sealed-battery CO710 above; for the second, also the CO710 — and if the real concern is chronic exposure at single-digit levels you are looking for a low-level monitor, which is a different instrument entirely.
- Backlit display shows the level of CO the alarm is sensing, rather than only sounding
- Plug-in with AA battery backup, so it keeps monitoring through a power cut — which is exactly when generators come out
- Rotating plug fits a vertical or a horizontal outlet, with published power-surge immunity
- No low-battery chirps, and one test/hush button for quick checks
- Kidde does not publish a peak-level memory for this model, and no current Kidde CO alarm does
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3. A hallway you will actually read
First Alert CO615 Plug-In CO Alarm with Battery Backup
Outlet height puts the display where a human can see it without a stepladder.
- Listed to
- UL 2034
- Sensing / agent
- Electrochemical CO sensor
- Power / service life
- AC powered with battery backup
The underrated virtue of a plug-in CO alarm is that people actually look at it. A ceiling alarm is checked when it beeps; a wall unit at eye-ish height gets glanced at, which means an unusual reading gets noticed.
That makes this a good second or third unit in a house that already has combination alarms on the ceilings — somewhere on the route between the bedrooms and the stairs.
The failure mode is human. Plug-in devices in hallways get unplugged for vacuum cleaners and phone chargers. If you buy one, put a note on the socket, or pick the socket nobody uses.
What it does well
- AC powered with battery backup, so an outage does not silence it
- Digital display at outlet height — readable and testable without climbing
- Nothing to install: it plugs in
- A sensible second unit for a hallway where a ceiling alarm already covers smoke
The downside
- Outlet-bound placement
- A plug-in unit in a hallway is easy to unplug for a vacuum cleaner and forget
- Backup battery is a maintenance item
Do not buy this if: the room has no convenient outlet, or the outlet you would use is behind furniture. An alarm plugged in behind a sofa is neither audible nor readable.
- Plugs in at outlet height, which is where a hallway alarm is easiest to read and test
- Battery backup keeps it alive through an outage
- Digital display of the current reading
- Tied to an outlet position, so it cannot go wherever you like
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4. Travel, cabins and rooms with no power
Kidde KN-COPP-B-LPM Battery CO Alarm with Digital Display
Battery only with a display and peak memory — the portable option.
- Listed to
- UL 2034
- Sensing / agent
- Electrochemical CO sensor
- Power / service life
- Battery powered; 10-year unit life
The travel case for a CO alarm is real and under-appreciated. Rented cabins, older holiday lets and RVs are exactly where fuel-burning appliances are poorly maintained and where you have no idea what detection exists. A battery alarm with a display in a bag costs very little and has saved people.
It is also the right unit for a room in a house with no accessible outlet and no interest in ceiling work — a garage office, a basement corner, a workshop.
The replaceable battery is the honest downside. A sealed unit cannot be left flat; this one can, so it needs to be on the annual list. The home fire safety checklist has a place for it.
What it does well
- Battery only, so it goes anywhere — a cabin, a rental, a hotel room, an RV
- Digital display and peak-level memory, unusual in a battery unit
- Genuinely portable, which more people should take advantage of
- No outlet, no wiring, no compromise on where it sits
The downside
- Replaceable batteries mean an actual annual maintenance task
- No mains power, so a flat battery is a silent failure
- Less convenient than a sealed unit for a permanent install
Do not buy this if: you want a fit-and-forget permanent alarm. For that the sealed-battery CO710 is the better answer — this one's advantage is that it travels.
- Battery only, so it goes where there is no outlet — a bedroom wall, a cabin, a rental
- Digital display plus peak-level memory
- Portable enough to travel with, which matters more than most buying guides admit
- Replaceable batteries mean an annual check is genuinely required
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Where to go next in this hub
This page is the general answer. Three narrower ones are often more useful. Best battery carbon monoxide detectors covers the case where the alarm has to go at the height a bedroom needs rather than wherever the socket is, and best carbon monoxide detectors under $50 is the page to read if a price cap is the constraint - in this category it costs you almost nothing, and even a low-level alarm fits under it.
For the room where a gas appliance runs a few feet from where you stand, best carbon monoxide detectors for kitchens covers the positions and the clearance. And if your CO coverage is bundled into combination alarms, Kidde smoke alarm alternatives is the page for replacing a retired model without losing the interconnect.
Where they go
One per level, and within earshot of every sleeping area. Carbon monoxide poisoning most often kills people who were asleep, so the position that matters is the one that wakes them. The sleeping areas have their own picks and their own criteria — night legibility, mounting freedom and whether a closed door costs you the decibels: best CO detectors for bedrooms.
One in or near the space with the furnace or water heater — but not mounted directly above the appliance, where the start-up plume will nuisance-trip it. That room has its own picks: best CO detectors for basements.
On the house side of a shared wall with an attached garage. A car started in an attached garage is one of the commonest residential CO events, and it does not require the car to be left running long.
High or low is the wrong question. CO has nearly the same density as air: it neither pools at the floor like propane nor collects at the ceiling like smoke. It mixes and travels with air currents and with the warm gas it arrives in, which is why manufacturers' instructions differ and why there is no single satisfying answer. Follow the instructions for your specific unit, keep alarms out of dead air within about 6 in of a ceiling-wall corner, and put them where you will hear them. Where to install CO detectors works through each room.
Who should not buy any of these
If you have no working smoke alarms, buy those first. It is not close: smoke alarms are the single highest-impact purchase in home fire safety, and a house with CO detection and no smoke detection has its priorities inverted. The smoke alarm roundup.
If you want CO and smoke detection from the same ceiling positions, buy combination alarms instead of separate units — fewer devices, fewer dates to track, one thing to replace. The trade-off is that a combination unit is replaced when either sensor ends its life. Combo versus separate works it through.
If your concern is chronic low-level exposure rather than acute poisoning — because someone in the household is pregnant, an infant, elderly or has a cardiac or respiratory condition — a UL 2034 alarm will not do what you want, by design. Buy one anyway, and add a low-level monitor. Best low-level CO monitors.
Questions people actually ask
What is the best carbon monoxide detector for a home?
Why does my CO detector read zero when I think there is carbon monoxide?
How many carbon monoxide detectors do I need?
Should a CO detector have a digital display?
Do carbon monoxide detectors expire?
Can I put a carbon monoxide detector next to the furnace?
How these picks were chosen. On published specifications, safety listings and manufacturer documentation — plus the findings of organizations that do run tests. We have no laboratory and we do not burn anything. Read the full methodology.
Sources
- UL Solutions — UL 2034 — single and multiple station carbon monoxide alarms
- CPSC — Carbon monoxide alarm conformance testing to UL 2034
- NFPA Fire Protection Research Foundation — A review of carbon monoxide alarm and detection thresholds
- CPSC — Carbon Monoxide Fact Sheet
- NFPA — NFPA 72, National Fire Alarm and Signaling Code (2025 edition)
Read next
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Combination Alarms vs Separate Units
One device or two — the replacement-timing trade nobody mentions.
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Carbon Monoxide Poisoning Symptoms
The symptoms, the flu-without-fever pattern, and the emergency action first.
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CO Detector Lifespan and Replacement
7-10 years from the manufacture date, why the test button proves little, and what END means.
Smoke Detectors
The Best Combination Smoke and CO Alarms
Two listings, one position — and the one room where separate units win.