First Alert carbon monoxide detector CO400 — 1-pack battery-operated, 5-year sensor, 85 dB alarm

This single-pack CO alarm from First Alert uses an electrochemical sensing element — a technology known for stable, accurate detection of carbon monoxide — and runs on a replaceable 9V battery so it works during power outages. The unit is ready to place on a shelf or mount on a wall with the included bracket; no hardwiring is needed. A test/silence button verifies operation and temporarily quiets nuisance alerts, while audible and visual low-battery warnings tell you when to change the battery.

How does the CO400 detect carbon monoxide and how long does it last?

The CO400 employs an electrochemical sensor that reacts specifically to CO gas, producing reliable readings over its service life. The sensor is permanent for the detector and is rated to last up to five years before replacement is recommended.

• Electrochemical sensor technology for accurate CO detection.
• Sensor lifespan: up to 5 years.
• End-of-life chirp alerts when the unit needs replacement.

What power source does it use and what happens during outages?

This model is powered by a single 9V replaceable battery, so it continues monitoring even when household power fails. The unit issues audible and visual battery warnings so you can replace the battery before protection is lost.

• Runs on one 9V replaceable battery (included or user-supplied).
• Maintains monitoring through electrical outages.
• Low-battery signals include both sound and visual indicator.

How loud is the alarm and can I test or silence it?

The CO400 sounds an 85-decibel horn when carbon monoxide levels reach alarm thresholds, loud enough to wake a sleeping household. A combined test/silence button allows you to check that the detector is functioning and to temporarily silence non-emergency chirps.

• 85 dB alarm for effective wake-and-notice capability.
• Test/silence button for quick functional checks and temporary silencing.
• Unit will re-alarm if dangerous CO levels persist after silencing.

Where should I place the CO400 and how many do I need?

Place one detector on each level of your home and outside sleeping areas for broad coverage; a detector in each bedroom is recommended for maximum safety. The CO400’s compact design lets you set it on a tabletop or use the optional wall mount—no electrical outlet required.

• Suitable for bedrooms, hallways, basements, and utility areas.
• No hardwiring—ideal for rental units and temporary needs.
• Use one per floor and one outside each sleeping area for best coverage.

Who is this for? Homeowners, renters, and landlords who want a simple, battery-operated carbon monoxide detector with proven electrochemical sensing and a five-year service life will find the First Alert CO400 a practical choice. It’s especially useful where hardwiring isn’t possible or for supplemental protection in bedrooms and finished basements. UL-listed and backed by First Alert’s home-safety experience, the CO400 offers straightforward installation, clear status alerts, and a compact profile for versatile placement.