Where should a CO alarm be installed?

Install CO alarms on every level of the home, including inside or directly outside each sleeping area. The NFPA 720 and most local codes require CO alarms within 10 feet of each sleeping room. Avoid installation near stoves, fireplaces, or vents where false alarms may occur due to normal combustion drafts.

What CO level triggers an alarm?

UL 2034 requires CO alarms to sound within specific time windows: alarm within 35 minutes at 150 ppm CO, within 15 minutes at 200 ppm CO, and within 4–15 minutes at 400 ppm CO. The alarm will NOT sound at concentrations below 70 ppm for more than 60 minutes — low-level chronic exposure monitoring requires industrial CO detectors.

How long does a CO alarm last before replacement?

Most residential CO alarms have a rated service life of 5–7 years. The electrochemical CO sensor degrades over time and must be replaced at end of life. The alarm's end-of-life warning (a distinct chirp pattern) indicates the unit must be replaced, not just the battery. Check the date of manufacture on the back of the unit.

What should I do when my CO alarm sounds?

Immediately evacuate all occupants from the building. Do not re-enter. Call 911 or your local fire department from outside. Do not assume the alarm is a false alarm. CO is odorless and colorless — the alarm may be the only warning. Seek medical attention if anyone experiences headache, dizziness, nausea, or confusion.

Does this CO alarm require a battery or hardwire installation?

See the product specifications for power requirements. First Alert CO alarms are available in battery-operated (9V or AA), plug-in, plug-in with battery backup, and hardwire with battery backup configurations. Battery backup is important for hardwired models to ensure protection during power outages.

Can a CO alarm detect gas leaks (natural gas or propane)?

No. Carbon monoxide (CO) alarms detect CO specifically — they do not detect natural gas, propane, or other combustible gases. For gas leak detection, install a combustible gas detector (methane/propane detector). These are separate devices with different sensor technologies.

First Alert CO400 Battery-Powered Carbon Monoxide Alarm with 9V Battery

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First Alert CO400 Battery-Powered Carbon Monoxide Alarm with 9V Battery

Name: First Alert CO400 Battery-Powered Carbon Monoxide Alarm with 9V Battery
Brand: First Alert

First Alert Carbon Monoxide Alarm GTIN: 029054000699

★ ★ ★ ★ ★ 4.8

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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9V battery carbon monoxide alarm CO detector CO400 First Alert

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.

Brand / Vendor

First Alert

Model / SKU

—

Product Type

Carbon Monoxide Alarm

Rating

4.8 / 5 — reviews

Availability

✓ In Stock on Amazon

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