First Alert CO250 Battery Carbon Monoxide Alarm with Tamper-Resistant Cover

What to check before you buy

UL 2034 listing

Residential CO alarms in the US are listed to UL 2034. Industrial CO monitoring is a different class of instrument with different alarm thresholds.

Alarms expire

CO sensors have a finite life - commonly 7 to 10 years from manufacture. Many units now sound an end-of-life chirp and cannot be reset.

Placement

CO mixes with air rather than layering at the ceiling like smoke, so alarms go on every level and outside sleeping areas. Keep them away from fuel-burning appliances and vents to reduce nuisance alarms.

Digital display

A display showing parts per million lets you distinguish a low-level chronic leak from a spike, which matters when talking to responders.

How it compares to other carbon monoxide alarms we review

List prices recorded when this page was last updated; Amazon pricing moves frequently, so check the live listing. Browse the full carbon monoxide alarms range.

Frequently asked questions

Where should CO alarms be installed?

On every level of the home and outside each sleeping area. Because CO mixes fairly evenly with air, height placement is less critical than it is for smoke alarms - follow the manufacturer instructions.

How long does a CO alarm last?

The electrochemical sensor has a limited life, commonly 7 to 10 years from the date of manufacture. Most modern units chirp at end of life and must be replaced, not reset.

What CO level is dangerous?

UL 2034 alarms are designed to respond to rising concentration over time, sounding faster at higher levels. Any alarm should be treated as real: get everyone outside and call emergency services.

Is a CO alarm the same as a smoke alarm?

No. They detect entirely different hazards. Combination units exist, but a smoke alarm alone offers no protection against carbon monoxide.

Why does my CO alarm chirp?

A single periodic chirp is usually low battery or end of sensor life; a repeating alarm pattern is a CO event. Check the manual for the specific pattern before assuming it is a battery.

Where do the specifications on this page come from?

They are taken from the manufacturer's published listing. WC Safety does not laboratory-test products, and nothing is claimed here that the manufacturer does not state.

Does WC Safety sell this product?

No. WC Safety is an independent review site and an Amazon Associate. Purchases happen on Amazon, and we earn a commission on qualifying purchases at no extra cost to you.