First Alert carbon monoxide detector 2-pack CO400 — battery powered, electrochemical sensor, 85 dB alarm

First Alert CO400 is a battery-powered carbon monoxide alarm 2-pack that uses electrochemical sensors to detect CO and sounds an 85-decibel alert when dangerous levels are present.

These two plug-free detectors are built for quick setup and continuous monitoring: insert the included 9V batteries, place a unit on each level or in bedrooms, and rely on the electrochemical sensor for accurate CO detection up to the sensor’s expected service life. The CO400 pair is UL-listed, includes a test/silence button, has a five-year expected sensor life, and provides audible and visual low-battery and end-of-life warnings. No wiring or electrician is required, and optional wall mounts let you position devices where you need them most.

How does the CO400 identify carbon monoxide in my home?

The CO400 uses an electrochemical sensor designed to respond to carbon monoxide molecules in the air. When concentrations reach predefined thresholds, the detector triggers its 85-decibel horn and will re-alarm if levels persist.

• Electrochemical sensing technology for reliable CO detection.
• 85 dB alarm provides a loud, clear alert across rooms.
• Automatic re-alarm if CO levels remain elevated.
• Visual indicators and audible chirps for low battery and end-of-life.

What’s required to install and maintain these battery-operated alarms?

Installation is tool-free: insert each included 9V battery, place or mount the unit, and press the test/silence button to confirm operation. Routine checks and timely battery replacement keep the alarm ready.

• 9V battery included per unit; battery access is on the back.
• Test/silence button lets you verify functionality and silence nuisance alerts.
• Optional wall mount snaps on—no outlet or wiring needed.
• Audible and visual low-battery signal prompts prompt battery changes.

How long will each CO400 detector provide protection before replacement?

Each CO400 detector uses a permanent electrochemical sensor with an expected service life of up to five years; the unit will emit an end-of-life chirp when replacement is recommended.

• Electrochemical sensor life typically up to five years.
• End-of-life signal reminds you when to replace the detector.
• 5-year limited manufacturer warranty for added reassurance.
• UL listed and compliant with current CO laws in several states.

Where should I place these CO alarms around my home?

Because carbon monoxide disperses evenly, place a CO400 on every sleeping level and inside or near bedrooms so occupants will hear the alarm while asleep. Avoid installing directly above fuel-burning appliances where occasional fumes can trigger nuisance alarms.

• Install one detector on each floor of the home.
• Place a unit in or just outside each bedroom for sleeping area coverage.
• Keep some distance from stoves, furnaces, or vent outlets to reduce false alarms.
• Use the optional wall mount to secure units at recommended heights.

Who is this for: Homeowners, renters, and property managers who want a simple, reliable, no-wiring carbon monoxide solution will find the First Alert CO400 2-pack practical and easy to deploy. It suits people who prefer battery backup for continuous monitoring during outages and those who need compact, UL-listed detectors that offer audible, visual, and end-of-life alerts without professional installation.