First Alert CO615 review: a plug-in CO alarm that keeps watching on AA batteries when the grid fails

This is a research-based review, based on manufacturer specs and published data. We do not test products. Specs come from First Alert's product page for the Plug-In Carbon Monoxide Alarm with Battery Backup and Digital Display (CO615), checked November 1, 2026. Safety guidance comes from the CDC, the Consumer Product Safety Commission (CPSC) and Ready.gov.

Carbon monoxide risk climbs during a long power outage. Generators, camp stoves, propane heaters and idling cars all make CO, and people reach for them exactly when the grid is down. A CO alarm that depends on wall power alone would go silent at the worst moment. The CO615 avoids that with two AA batteries that take over when the outlet goes dead.

One fact shapes this review: First Alert's own page now lists the CO615 as discontinued. Retail listings may still carry it. That does not make it unsafe, but it does mean you should check what you are buying and know when the unit will reach the end of its life.

Who should buy it

• Households that want a CO reading at bed height. The 6 ft cord lets the alarm sit on a nightstand while the plug stays in a low outlet.
• People who like to see a number. The backlit display shows the CO level and the backup battery level, readable in the dark.
• Anyone adding a second or third alarm near bedrooms, where a generator or propane heater may run during an outage.

Who should skip it

• Anyone who will not keep AA batteries fresh. In an outage the backup cells are the only power. A sealed 10-year model such as the First Alert CO710 or the Kidde COBD10 removes that chore.
• Buyers who need a model the maker still lists for sale. For a current plug-in alternative, look at the Kidde COPD or the Eton Blackout Buddy CO.
• People who want interconnected alarms. First Alert does not describe interconnection for the CO615.

Strengths

• Keeps working in a blackout. Two AA cells back up the outlet power, and First Alert says the backup provides protection during power outages.
• Corded, not a wall wart. The 6 ft power cord means it can sit on a shelf or nightstand instead of at knee height behind furniture.
• A number, not just a siren. The backlit display shows CO level and backup battery level, and First Alert says it gives off a soft blue light suited to bedrooms.
• Loud enough to wake people. 85 dB at 10 feet, the figure First Alert lists for its alarm.
• Clear warnings. A low-battery indicator light and audible signal tell you when the AA cells need changing, and an end-of-life warning tells you when to replace the unit.
• 7-year limited warranty, per First Alert.

Drawbacks

• Discontinued. First Alert's page lists the CO615 as discontinued. Stock on shelves may be older, and the end-of-life clock may have started. Check the manufacture date on the back of the unit.
• Battery chore. The backup cells are replaceable, which means someone has to replace them. Dead backups make it a plug-in-only alarm in a blackout.
• Sensor life not listed. The product page gives an end-of-life warning but no sensor life figure, so read the manual that comes in the box.
• Cord placement. It needs an outlet within 6 feet of where you want it, and the cord itself needs a safe route.

How it compares

The CO615 against three alarms that also keep working without grid power. Figures are from each manufacturer's page, checked November 1, 2026.

Using it in a long outage

Set it up before an outage

1. 01Put fresh AA batteries in the backup compartment and write the date on a piece of tape inside the battery door.
2. 02Plug it in and press the test/silence button to confirm the alarm sounds.
3. 03Check the manufacture date on the unit. If it is old stock, plan its replacement around the end-of-life warning.
4. 04Put spare AA cells for the alarm in a bag that is not raided for flashlights.

Where it should sit when fuel is burning

Ready.gov advises carbon monoxide detectors with battery backup in central locations on every level of the home. In an outage, think about where combustion is happening. Put one alarm in or near each sleeping area, and another in any room where an indoor-rated propane heater such as the Mr. Heater Portable Buddy is running. The CO615's cord makes the bedroom placement easy: set it on the nightstand on the side nearest the door.

Know the symptoms

The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion as the most common symptoms of CO poisoning, and says people who are sleeping or drunk can die before they have symptoms. That is why the alarm matters most at night. If more than one person feels sick at the same time, treat it as CO, get out and call for help from outside.

Through a long outage

Once the outlet is dead, the AA cells run everything, including the backlight. Check the display once a day. If the low-battery light or chirp starts, swap in the spare set right away rather than waiting for daylight. The CPSC's Carbon Monoxide Information Center is worth reading before winter for its generator and heater rules.

For a full comparison of sealed and plug-in models, see our best carbon monoxide alarms guide.