Search  for anything...

First Alert CO400 Carbon Monoxide (CO) Detector, Battery Operated Alarm, 1-Pack

  • Based on 20,307 reviews
Condition: New
Checking for the best price...
$22.49 Why this price?
Save $46.48 was $68.97

Buy Now, Pay Later


As low as $5 / mo
  • – 4-month term
  • – No impact on credit to apply
  • – Instant approval decision
  • – Secure and straightforward checkout

Ready to go? Add this product to your cart and select a plan during checkout.

Payment plans are offered through our trusted finance partners Klarna, Affirm, Afterpay, Apple Pay, and PayTomorrow. No-credit-needed leasing options through Acima may also be available at checkout.

Learn more about financing & leasing here.

Selected Option

Free shipping on this product

FREE 30-day refund/replacement

To qualify for a full refund, items must be returned in their original, unused condition. If an item is returned in a used, damaged, or materially different state, you may be granted a partial refund.

To initiate a return, please visit our Returns Center.

View our full returns policy here.


Availability: Only 8 left in stock, order soon!
Fulfilled by Amazon

Arrives Thursday, Jun 18
Order within 4 hours and 6 minutes
Available payment plans shown during checkout

Protection Plan Protect Your Purchase
Checking for protection plans...

Size: Pack of 1


Pattern Name: Detector


Features

  • Keep your family safe with this easy to use, battery operated carbon monoxide alarm; Battery powered alarms provide continuous monitoring of CO levels, even if there's a power failure
  • Features an advanced electrochemical carbon monoxide sensor that accurately detects carbon monoxide levels, no matter where the detector is placed in the room.The alarm sequence should last 5-6 seconds. If it does not alarm, make sure fresh batteries are correctly installed, and test it again. If the unit still does not alarm, replace it immediately
  • A loud 85 decibel alarm sounds when CO levels reach dangerous , Battery Replaceable - Yes
  • To ensure complete protection make sure to place one on each level of your home and in each bedroom
  • 5-year limited warranty; Equipped with end of life signal chirp, so you know when its time to replace the unit for safety
  • All first alert CO alarms are rigorously tested to meet UL standards
  • First Alert has been the most trusted brand in home safety since launching the first residential smoke alarm in 1958 (Based on a First Alert Brand Trust Survey in February 2018)

Description

The First Alert CO400 carbon monoxide alarm uses an electrochemical sensor the most accurate technology available. The permanent sensor lasts up to 5 years. It is powered by a 9V replaceable battery giving you peace of mind even during power outages. The test/silence button silences the alarm and allows you to test its functionality. The unit monitors and re alarms if carbon monoxide level persist sounding a loud 85 decibel horn. No installation is required and the attractive design allows the unit to be placed anywhere you need it. It includes an optional wall mount with no outlet required. An audible and visual battery signal alerts you to replace the battery. Pull down action chart has convenient guide on what to do if an alarm sounds. 5 year limited warranty. Ul listed. Carbon monoxide (CO) is the leading cause of accidental poisoning deaths in America, yet many people don't know they are suffering from CO poisoning until its too late. Since symptoms of CO poisoning are like the flu, you might not even know you're in danger at first. That's why a carbon monoxide alarm is an excellent way to protect your family. It can detect the CO you can't see, smell or taste in the air. The First Alert CO400 carbon monoxide alarm uses an electrochemical carbon monoxide sensor-the most accurate technology available. The permanent sensor lasts up to five years. It is powered by on 9V replaceable battery giving you peace of mind even during power outages. The test/silence button both silences the alarm and allows you to test its functionality. The unit monitors and re-alarms if carbon monoxide levels persist sounding a loud 85-decibel horn. No installation is required and the attractive design allows the unit to be placed anywhere you need it. It includes an optional wall mount with no outlet required. An audible and visual low battery signal alerts you to replace the battery. Pull down action chart has convenient guide on what to do if an alarm sounds. 5 year limited warranty. UL listed. --Bree Norlander P.when('A').execute(function(A) { A.on('a:expander:toggle_description:toggle:collapse', function(data) { window.scroll(0, data.expander.$expander[0].offsetTop-100); }); }); Manufacturer Contact Information . See more

Brand: First Alert


Style: Battery Powered


Power Source: Battery Powered


Color: White


Product Dimensions: 1"D x 5"W x 3"H


Item Weight: 7.2 ounces


Alarm: Audible


Operating Humidity: 10-95% RH


Sensor Type: Electrochemical


Global Trade Identification Number: 99


Power Source: Battery Powered


Alarm: Audible


Sensor Type: Electrochemical


Operating Humidity: 10-95% RH


Product Style: Battery Powered


Color: White


Item Dimensions D x W x H: 1"D x 5"W x 3"H


Item Weight: 7.2 ounces


Enclosure Material: Multi


Brand: First Alert


Model Number: CO400


Global Trade Identification Number: 99


Manufacturer Warranty Description: 5 Year Limited Warranty


Number of Items: 1


Manufacturer: First Alert


UPC: 029054000699


Mfr Part Number: CO400


Unit Count: 1.0 Count


Item Type Name: First Alert CO400FF Battery Powered Carbon Monoxide Alarm


Built-In Media: Alarm; Mounting Bracket; User Manual; 9V Battery


Manufacturer Contact Information: .


Frequently asked questions

If you place your order now, the estimated arrival date for this product is: Thursday, Jun 18

Yes, absolutely! You may return this product for a full refund within 30 days of receiving it.

To initiate a return, please visit our Returns Center.

View our full returns policy here.

  • Klarna Financing
  • Affirm Pay in 4
  • Affirm Financing
  • Afterpay Financing
  • PayTomorrow Financing
  • Financing through Apple Pay
Leasing options through Acima may also be available during checkout.

Learn more about financing & leasing here.

Top Amazon Reviews


  • Simple, reliable, and essential for home safety
Size: Pack of 1 Pattern Name: Detector
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. ... show more
Reviewed in the United States on May 20, 2026 by Jeff S.

  • Great Carbon Monoxide Detector – Easy to Install and Reliable!
Size: 2 Count (Pack of 1) Pattern Name: Detector
I bought two of the First Alert Carbon Monoxide Detectors (model CO400), and I’m very happy with them. They were super easy to install — no outlet needed since they run on batteries. I just mounted them on the wall, and they were ready to go in minutes.I like that the battery operation means I can place them anywhere in my home without worrying about finding a plug. The alarm is loud enough to hear clearly, and the design is compact and simple.It gives me peace of mind knowing my family is protected. Overall, great value, easy setup, and reliable safety product. Highly recommend! ... show more
Reviewed in the United States on November 12, 2025 by Jean

  • Great Value for Peace of Mind
Size: 2 Count (Pack of 1) Pattern Name: Detector
Great Value, easy to set up, peace of mind! Alarm is loud and indicator light functions well.
Reviewed in the United States on May 30, 2026 by HonestlyMe

  • great value and easy to set up
Size: 2 Count (Pack of 1) Pattern Name: Detector
GREAT PRODUCT .GOOD PRICE
Reviewed in the United States on June 4, 2026 by Amazonaddict

  • Battery operated only
Size: Pack of 1 Pattern Name: Detector
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.
Reviewed in the United States on May 30, 2026 by Melissa

  • Works as advertised reasonable price.
Size: Pack of 1 Pattern Name: Detector
Great product lots of instructions easy to install
Reviewed in the United States on April 28, 2026 by Richard B. Oregon

  • Second purchase
Size: Pack of 1 Pattern Name: Detector
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!
Reviewed in the United States on May 19, 2026 by Vilma

  • Small Device, Big Peace of Mind Small Device, Big Peace of Mind
Size: 2 Count (Pack of 1) Pattern Name: Detector
I always pack a compact carbon monoxide detector when I travel—it’s small enough to slip into my luggage without a second thought, but the peace of mind it provides is huge. Whether I’m staying in a hotel or an Airbnb, it’s reassuring to know I have an extra layer of safety in an unfamiliar space. It’s one of those tiny items that takes up almost no room, yet feels absolutely essential once you start bringing it along. ... show more
Reviewed in the United States on March 25, 2026 Reviewed in the United States on March 25, 2026 by TexMexJess

Can't find a product?

Find it on Amazon first, then paste the link below.
Checking for best price...