Message to Our Customers

First Alert

Model # CO400

Internet # 202433876

Battery Powered Carbon Monoxide Alarm

This item has been discontinued.
The Home Depot no longer carries this specific product.

$14.78 / each


Model # CO400

Internet # 202433876

The First Alert CO400 battery powered carbon monoxide detector with mute button is an easy-to-install, UL-listed alarm that combines advanced technology with a user-friendly design. Symptoms of carbon monoxide poisoning are like the flu, and you might not even know you're in danger. That's why a carbon monoxide alarm is an excellent way to protect your family. It detects the CO you can't see, smell or taste in the air. A single button tests alarm functions and mutes nuisance alarms. This alarm uses an electrochemical carbon monoxide sensor, which is the most accurate technology available. With battery backup, you will have peace of mind that the alarm will continue to work even when the power goes out. It's esthetically pleasing premium shape is ideal for placing in all visible location. The easy loading back access battery door allows you to quickly and easily change the alarms single 9-Volt battery. 5-year limited warranty. Meets UL standards and is code compliant.

  • Battery powered carbon monoxide detector
  • Single button tests alarm functions and silences nuisance alarms
  • EZ access back loading battery door for 9-Volt batteries
  • Low battery warning
  • End of detector life timer
  • 9-volt battery included
  • Utilizes an electrochemical sensor, the most accurate technology to detect carbon monoxide
  • 5-year limited warranty
  • Meets UL2034 standard
  • Loud 85db alarm
  • America's most trusted brand in home safety
  • Note: Product may vary by store

Info & Guides

You will need Adobe® Acrobat® Reader to view PDF documents. Download a free copy from the Adobe Web site.


Product Depth (in.) 
Product Height (in.) 
Product Width (in.) 
Alarm Type 
Carbon Monoxide 
Alarm/Detector Features 
No Additional Features 
Battery Back-Up 
Commercial / Residential 
Commercial / Residential 
Connector/Contact Type 
Power Source 
Voltage (volts) 
Warranty / Certifications
Certifications and Listings 
1-UL Listed 


Rated 3.8 out of 5 by 21 reviewers.
Rated 5.0 out of 5.0 by This product has a low profile and installs easily into any environment. This carbon monoxide detector has a mute button and is easy-to-install, not to mention it was priced right. April 30, 2013
Rated 2.0 out of 5.0 by Supplied Instrustions Need Revision The warning label material for CO alarm is too shiny to write on with a ball point pen. Writing smeared. Use a SHARPIE PERMANENT MARKER. The instructions to mount the unit on a wall state, "Hold the mounting guide....". There is no mounting guide! The warranty section states, "....warrants that for a period of seven years.....", and the package states "5 YEAR LIMITED WARRANTY'. Which is it????? Please forward to FIRSTALERT. Their website has no email address to inform them. A phone call would not provide me with verification. February 10, 2015
Rated 5.0 out of 5.0 by Carbon Monoxide Alarm Nice design and very easy to install. Clear instructions. May 12, 2015
Rated 4.0 out of 5.0 by clean and simple. easy to install Product delivered to store according to schedule. Easy pick up and met competitors price, although it was a tedious process to accomplish this. Would order store delivery again April 23, 2014
Rated 4.0 out of 5.0 by Dead Battery; Orange "ok" light. Battery supplied with detector was dead on arrival. It is also disturbing that it has an orange flash indicating its working rather than the green normally seen on smoke detectors. Orange usually indicates something is wrong. August 19, 2014
Rated 5.0 out of 5.0 by I love it Very easy to install, directions were great. Looks good. May 13, 2014
Rated 5.0 out of 5.0 by Good product Was all I expected it to be. Have these items in my home already, just adding more. Am very pleased. May 9, 2012
Rated 1.0 out of 5.0 by Battery compartment door is awful. Bought two of these and tried to install the batteries, but a piece of plastic inside the doors keeps them from closing when the batteries are in place (and even dented one). I called First Alert, and they said others have had the same issue, and breaking that piece off makes it worse. They recommended I return both and made no apologies. We needed these alarms because our heater is quite old but unfortunately they are unusable. January 28, 2014
  • 2015-05-21T12:12:05.122-05:00
  • bvseo_lps, prod_bvrr, vn_prr_5.6
  • cp-1, bvpage1
  • co_hasreviews, tv_21, tr_21
  • loc_en_US, sid_202433876, prod, sort_default
2 >>


Standard Shipping includes delivery by small parcel service. Processing time varies by product.

If product is eligible for shipping to AK, HI and US Territories additional transit time and remote surcharges may apply.