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First Alert CO400 Battery-Powered Carbon Monoxide Alarm with 9V Battery
$22.49
Final price set by Amazon · may vary
Short answer: The CO400 is First Alert's entry-level battery-powered CO alarm — powered by a single 9V battery, no outlet required, place it anywhere. If you need a no-frills detector for a bedroom, RV, camper, or a l...
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Short answer: The CO400 is First Alert's entry-level battery-powered CO alarm — powered by a single 9V battery, no outlet required, place it anywhere. If you need a no-frills detector for a bedroom, RV, camper, or a location away from outlets, the CO400 is the right choice. If you have AC power available and want a permanent installation, the CO606 (plug-in with battery backup) is a better long-term option.
Key specs at a glance
- Power: 1 × 9V battery (included)
- Sensor: Electrochemical CO sensor
- Alarm Output: 85dB at 10 feet
- Listing: UL 2034 — the required standard for residential CO alarms
- Warranty: 5-year limited
- Operation: Single test/silence button
CO400 vs CO600 vs CO606 — Which One to Buy
| Model | Power | Backup | Warranty | Best For |
|---|---|---|---|---|
| CO400 ★ | 9V battery | N/A | 5 yr | No-outlet locations, RVs, supplemental use |
| CO600 | AC plug-in | None | 7 yr | Near-outlet permanent install, no outage concern |
| CO606 | AC plug-in | 9V battery | 7 yr | Permanent install with power outage protection |
Where to Place a CO Alarm
- Outside every sleeping area: NFPA 720 and most local codes require CO alarms on each level and outside each sleeping area
- Each level of the home: CO can accumulate on any floor depending on source location
- Near attached garages: Vehicle exhaust is a major residential CO source
- Not in kitchens or near cooking appliances: Combustion products from normal cooking can trigger false alarms
- Not in high-humidity areas: Steam from bathrooms can shorten sensor life
Frequently Asked Questions
How long does the battery last?
First Alert states the CO400 provides approximately 1 year of battery life from a standard 9V alkaline battery. The unit will chirp to indicate a low battery before protection is lost.
Does the CO400 also detect smoke?
No — the CO400 detects carbon monoxide only. For complete protection, pair it with a separate smoke alarm. First Alert offers combination smoke/CO alarms if you prefer a single unit.
When does the alarm trigger?
Per UL 2034 requirements, the CO400 alarms based on CO concentration over time: 70 ppm for 1–4 hours, 150 ppm within 10–50 minutes, or 400 ppm within 4–15 minutes. It will not alarm at CO levels below 70 ppm, which prevents false alarms from brief ambient exposure.
Is the CO400 required by code?
CO alarm requirements vary by state and locality. As of 2026, most states with CO alarm laws require detectors outside sleeping areas and on each level. Check your local building or fire code — many jurisdictions now require CO alarms in all new construction and rental properties.
How do I know when to replace it?
The CO400 has a 5-year warranty and the electrochemical sensor has a limited lifespan. After 5–7 years, the sensor degrades and the unit should be replaced. First Alert builds in an end-of-life warning chirp pattern that differs from the low-battery chirp.
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What to check before you buy
- UL 2034 listing
- Residential CO alarms in the US are listed to UL 2034. Industrial CO monitoring is a different class of instrument with different alarm thresholds.
- Alarms expire
- CO sensors have a finite life - commonly 7 to 10 years from manufacture. Many units now sound an end-of-life chirp and cannot be reset.
- Placement
- CO mixes with air rather than layering at the ceiling like smoke, so alarms go on every level and outside sleeping areas. Keep them away from fuel-burning appliances and vents to reduce nuisance alarms.
- Digital display
- A display showing parts per million lets you distinguish a low-level chronic leak from a spike, which matters when talking to responders.
How it compares to other carbon monoxide alarms we review
| Product | List price |
|---|---|
| First Alert CO400 Battery-Powered Carbon Monoxide Alarm with 9V Battery (this page) | $22.49 |
| Kidde COB Battery-Powered Carbon Monoxide Alarm | $26.97 |
| Kidde COP Plug-In Carbon Monoxide Alarm with Battery Backup | $34.97 |
| Kidde COBD Carbon Monoxide Alarm, Portable AA with Digital Display | $31.97 |
| Kidde COPD plug-in carbon monoxide alarm | $43.97 |
| Kidde COB10 Carbon Monoxide Alarm, 10-Year Battery, LED Alarm-Only | $45.97 |
| Kidde COBD10 Carbon Monoxide Alarm, 10-Year Battery with Digital Display | $52.97 |
List prices recorded when this page was last updated; Amazon pricing moves frequently, so check the live listing. Browse the full carbon monoxide alarms range.
Frequently asked questions
Where should CO alarms be installed?
On every level of the home and outside each sleeping area. Because CO mixes fairly evenly with air, height placement is less critical than it is for smoke alarms - follow the manufacturer instructions.
How long does a CO alarm last?
The electrochemical sensor has a limited life, commonly 7 to 10 years from the date of manufacture. Most modern units chirp at end of life and must be replaced, not reset.
What CO level is dangerous?
UL 2034 alarms are designed to respond to rising concentration over time, sounding faster at higher levels. Any alarm should be treated as real: get everyone outside and call emergency services.
Is a CO alarm the same as a smoke alarm?
No. They detect entirely different hazards. Combination units exist, but a smoke alarm alone offers no protection against carbon monoxide.
Why does my CO alarm chirp?
A single periodic chirp is usually low battery or end of sensor life; a repeating alarm pattern is a CO event. Check the manual for the specific pattern before assuming it is a battery.
Where do the specifications on this page come from?
They are taken from the manufacturer's published listing. WC Safety does not laboratory-test products, and nothing is claimed here that the manufacturer does not state.
Does WC Safety sell this product?
No. WC Safety is an independent review site and an Amazon Associate. Purchases happen on Amazon, and we earn a commission on qualifying purchases at no extra cost to you.
Brand / Vendor
First Alert
Model / SKU
CO400
Product Type
Carbon Monoxide Alarm
Price
$22.49 (Amazon)
Rating
4.86 / 5 — 7 reviews
Availability
Check current availability on Amazon
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Verified Buyer Reviews
Customer Reviews
★★★★★4.6 / 5· 17,599 ratings on Amazon
★★★★★
Simple, reliable, and essential for home safety
I recently purchased this First Alert CO400 detector to add another layer of safety to my home, and I’m very satisfied with the experience.What I appreciate most is the straightforward, battery-operated design. It was incredibly easy to set up—no hardwiring or complex installation required, which makes it perfect for placing exactly where you need it without worrying about electrical outlets. The unit feels sturdy and well-built, and the alarm is loud and impossible to miss.It provides great peace of mind, especially given how unobtrusive and reliable it has been since I installed it. For anyone looking for a no-fuss, effective way to monitor carbon monoxide levels in their living space, this is a solid, must-have product.
Verified Purchaser · May 20, 20 · ✓ Amazon Verified Purchase
★★★★★
Works as advertised reasonable price.
Great product lots of instructions easy to install
Verified Purchaser · April 28, · ✓ Amazon Verified Purchase
★★★★★
Battery operated only
Works as expected. It does not plug in. Battery only. Wish I had read a little better, but good product if you only use batteries.
Verified Purchaser · May 30, 20 · ✓ Amazon Verified Purchase
★★★★☆
Good
I can't believe the prices on CO detectors!!! They are unnecessarily expensive. My current unit was over 10 years old and kept throwing error codes so it was time for a replacement. I ultimately decided on this First Alert as it is the same brand I have trusted for years. The price was affordable. I cannot attest to any longevity or functionality because an emergency has not come up. The "Test" button does work as expected.
Verified Purchaser · January 29 · ✓ Amazon Verified Purchase
★★★★★
Easy set up
easy set up. Peace of mind so inexpensive..
Verified Purchaser · June 10, 2 · ✓ Amazon Verified Purchase
★★★★★
Second purchase
I did see some negative reviews but I purchased this for the second time because I did not have any issues. The last one was reliable. Lasted over 10 years and the only chirp was end of life 5 chirps and replace battery. We are very comfortable this is doing its job!
Verified Purchaser · May 19, 20 · ✓ Amazon Verified Purchase
★★★★★
Awesome brand - confident
Feel like this is a well known and respected brand. Easy to install, testing of each one is simple by pushing a button.
Verified Purchaser · May 25, 20 · ✓ Amazon Verified Purchase
Showing 7 of 17,599 Amazon reviews.
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