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First Alert CO alarm chirping once a minute: the low battery warning

A single chirp about once a minute is the low battery warning on First Alert’s replaceable-battery CO alarms: fit new batteries. The light that comes with it differs by model: the CO400’s red light keeps flashing, the SCO5’s light flashes with each chirp. A sealed 10-year alarm such as the SMCO210 has no battery to change, so its low battery signal (5 chirps and one green flash a minute) means the whole alarm has to be replaced.

If it is sounding a full alarm: First Alert’s carbon monoxide instruction

Carbon monoxide alarm

First Alert (SCO5, SMCO210 and CO710 manuals): “If you hear the CO alarm horn and the CO red light is flashing, move everyone to a source of fresh air.” Then: press the Test/Silence button; “call your emergency services, fire department or 911”; “immediately move to fresh air—outdoors or by an open door or window” and do a head count. Do not go back in until the emergency services responder has arrived, the premises have been aired out and the alarm is back to normal. If it sounds again within 24 hours, repeat those steps and call a qualified appliance technician.

From Model SCO5 manual, Model SMCO210 manual, Model CO710 manual.

Low battery, model by model

3 First Alert models whose manuals we read. The model number is on the label on the back of the alarm. If yours is not here, its own manual is the authority: First Alert models do not all use the same lights.

ModelWhat you seeWhat you hear
CO400 battery CO alarm, one 9-volt batteryRed light keeps flashingOne chirp about every minute
SCO5 combination smoke and CO alarm, two AA batteriesLight flashes with each chirp (green once a minute while the chirp is silenced)One chirp about once a minute
SMCO210 combination smoke and CO alarm, 10-year sealed batteryOne green flash about every minute5 chirps every minute

First Alert CO400: battery CO alarm, one 9-volt battery

Red light keeps flashing; One chirp about every minute
What you see
Red light keeps flashing
What you hear
One chirp about every minute

“The light continues to flash (RED) and the horn ‘chirps’ once every minute. Low battery warning. Install 1 new 9 volt battery.”

CO400 user’s manual

What the CO400 manual says to do

  1. Fit one new 9-volt battery. The manual lists Duracell MN1604, Energizer 522 and Ultralife U9VL-J-P, and says “DO NOT use rechargeable batteries.”
  2. “The low battery warning should last for 7 days, but you should replace the battery immediately to continue your protection.”
  3. The Test/Silence button can quiet the low battery chirp “for up to 8 hours”; after that it comes back. Test the alarm after the battery change.

Source:

First Alert SCO5: combination smoke and CO alarm, two AA batteries

Light flashes with each chirp (green once a minute while the chirp is silenced); One chirp about once a minute
What you see
Light flashes with each chirp (green once a minute while the chirp is silenced)
What you hear
One chirp about once a minute

“Horn ‘chirps’ about once per minute. Low battery warning. Install two new AA batteries.”

SCO5 user’s manual

What the SCO5 manual says to do

  1. Fit two new AA batteries in the side drawer, matching + to + and − to −; the battery door resists closing without batteries.
  2. Silencing the chirp lasts up to 8 hours: “the unit continues to flash the Green light once a minute for 8 hours. After 8 hours, the low battery ‘chirp’ will resume.”
  3. “Replace the batteries as soon as possible; this unit will not operate without battery power!”

Source:

First Alert SMCO210: combination smoke and CO alarm, 10-year sealed battery

One green flash about every minute; 5 chirps every minute
What you see
One green flash about every minute
What you hear
5 chirps every minute

“If Battery Becomes Low — Horn: 5 chirps every minute; Power LED: One green flash approximately every minute. … Low Battery Signal, Alarm needs to be replaced. Immediately replace the Alarm.”

SMCO210 user’s manual

What the SMCO210 manual says to do

  1. Replace the alarm: the battery is sealed (“No Battery Replacements”).
  2. Before disposal, deactivate it: insert a tool below the edge, break the tab and slide the activation switch to deactivate. First Alert says this drains the stored energy and the unit will no longer work.
  3. Five green flashes with the same 5 chirps is the end of life signal instead; it also means replace.

Source:

Not the signal you have?

Sources

Every line on this page comes from First Alert’s own user’s manuals, read on the date shown; the quotes are the manuals’ words. firstalert.com’s product pages link these manuals as their downloads; the files are kept on the asset host of Resideo, which owns First Alert.

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