Kidde Carbon Monoxide Alarm Code L6: What It Means & What to Do

Kidde carbon monoxide alarm code “L6” is not a code listed in Kidde’s user guide or support pages; the documented low-battery signal is “Lb” (capital L, lower-case b), which is easy to read as “L6” on a small digital display. A letter code like Lb is a maintenance message about the alarm. A number on the display, or the four-beep alarm pattern, is not: that means leave the home and call 911. This guide lays out what each Kidde display and beep pattern means, using Kidde’s own tables for two common battery models.

What Does Code L6 Mean?

Kidde’s documented low-battery code is “Lb”, not “L6”. Kidde’s support page on the digital display says the capital L with a lower-case b is letting you know the battery is low and needs to be replaced. The Kidde CO alarm user guide for models KN-COB-B-LPM and KN-COPP-B-LPM (Manual P/N 21008094 Rev C), Kidde’s ERR message page and its beeping and chirping page list no “L6” code. So if your display looks like “L6”, compare it with the seven-segment “Lb” first, and check the model number and manufacture date on the back of the unit against your own manual.

Kidde digital display codes (model KN-COPP-B-LPM guide)

This table comes from the operating-characteristics chart in the KN-COPP-B-LPM user guide. Other Kidde models have their own charts, so use the manual for your model number.

Display shows	Sound	Kidde says it means	What the guide says to do
Steady number 30-999, red LED flashing with the beeps	4 quick beeps, 5 seconds of silence, repeating	Alarm condition: dangerous concentrations of CO	Follow “What to do When the Alarm Sounds” (see below)
“Lb” flashing alternately with a number, red LED every 60 seconds	One quick beep every 60 seconds	Batteries need to be replaced	Replace all three AA batteries immediately
“Err”	One quick beep every 30 seconds	Error condition	Replace batteries; if Err continues the unit has malfunctioned and must be replaced immediately, and it will not respond to CO
“End”, red LED flashing twice every 30 seconds	Two quick beeps every 30 seconds	End of unit life	Replace the unit immediately; it will not respond to CO
Blank display	Constant alarm	Unit malfunction	Call Kidde product support: 1-800-880-6788

The guide says “Lb” flashes alternately with any number, and a steady reading from 30 to 999 with the four-beep pattern is the alarm condition. Kidde’s rule for any digital unit: a number on the display, with or without an alert, means assume it senses carbon monoxide.

Is It Really “L6,” or Is Your Alarm Showing “Lb”?

Look at the character after the capital L. The low-battery message is an L followed by a lower-case b, which has a straight stem at the top, while a 6 has a curved top. On a small segmented display the two can be hard to tell apart in poor light, which is a likely reason people search for “L6”.

Use the beep pattern as a second check. In the KN-COPP-B-LPM guide, a low battery gives one quick beep every 60 seconds along with a red LED flash every 60 seconds. The Kidde support page on CO alarm beeping also lists a chirp once every 60 seconds as a possible low battery.

Decoding The Beeps

Kidde’s support page and the operating-characteristics charts in the KN-COB-B-LPM and KN-COPP-B-LPM guide show the patterns below.

What you hear	What it usually means (per Kidde)	Action
4 short beeps, 5 seconds of silence, 4 short beeps, repeating	Alarm: the unit may have detected carbon monoxide; Kidde also notes it could be a nuisance alarm	Treat as real. Leave and call 911
1 chirp every 60 seconds	Low battery (also listed by Kidde with other causes such as an error code on a display)	Replace the batteries as your manual directs
1 beep every 30 seconds	Error or service condition on the KN-COB-B-LPM and KN-COPP-B-LPM charts	Replace the batteries; if it continues, replace the unit
2 beeps every 30 seconds	End of unit life on the KN-COB-B-LPM and KN-COPP-B-LPM charts (10 years after power-up)	Replace the alarm immediately
One long, continuous squeal	Kidde lists a tamper-resist warning on plug-in units, or an alarm malfunction	Call Kidde product support: 1-800-880-6788

Kidde’s support page gives a chirp every 30 seconds as the end-of-life pattern for older units: seven years after initial power-up, the chirp will not stop until the unit is powered off, and new batteries will not stop it. Kidde’s replacement page says all Kidde CO alarms made since 2013 have a 10-year life, except models KN-COEG-3, KN-COPE-I and KN-COPP-3. The manufacture date is on the back of the alarm.

What To Do In Case Of A Carbon Monoxide Alert

The CDC lists headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion as the most common CO symptoms, often described as flu-like. The CPSC says that if you suspect CO poisoning you should get outside to fresh air immediately, and then call 911.

Kidde’s guide for the KN-COB-B-LPM and KN-COPP-B-LPM gives this procedure when the alarm sounds:

1. Operate the Test/Reset button.
2. Call your emergency services (Fire Department or 911).
3. Immediately move to fresh air, outdoors or by an open door or window, and do a head count. Do not reenter the premises nor move away from the open door or window until the emergency responders have arrived, the premises have been aired out, and your alarm remains in its normal condition.
4. If the alarm reactivates within 24 hours, repeat steps 1 to 3 and call a qualified appliance technician to look for CO from fuel-burning equipment and appliances.

The same guide says never to ignore the sound of the alarm, and that if it sounds again within six minutes of pressing Test/Reset, the unit is sensing high levels of CO. It also says to make sure motor vehicles are not, or have not been, operating in a garage attached or adjacent to the home.

The CDC says never to run a car or truck inside a garage attached to a house, even with the garage door open; see our guide on whether cars produce carbon monoxide. Kidde’s guide adds that you should never restart the source of a CO problem until it has been corrected.

How To Fix A Low-Battery “Lb” On A Kidde Digital Alarm

These steps apply to a battery-operated Kidde digital alarm such as the KN-COPP-B-LPM, and they come from that model’s guide. A different Kidde model may use a different battery type or a sealed battery, so check the manual for your model number first.

1. Slide open the bottom cover to expose the battery compartment.
2. Remove the old batteries and dispose of them as the battery maker recommends.
3. Install three new AA batteries, matching the polarity marks in the compartment. The cover will not close unless all three are installed.
4. Close the cover, reinstall the alarm, press Test/Reset and check that the green LED flashes about once every 30 seconds.

The guide lists approved batteries (Duracell MN1500 or MX1500, Energizer E91, Gold Peak 15A, Golden Power GLR6A) and warns that a different battery may have a detrimental effect on the alarm. It recommends replacing the battery at least once a year or at the daylight saving clock change; the CDC likewise says to check detector batteries when you change the clocks each spring and fall.

If the chirp continues after new batteries, or if it is the 30-second pattern, the unit is in an error or end-of-life state and Kidde says it must be replaced because it will not detect CO in those states.

When It Is Not The Battery: Err, End And Blank Displays

Kidde’s ERR page says an ERR message can mean an end-of-life warning after the alarm has been active for its 7- or 10-year life, a power surge, or a sensor error. Those last two have a first step:

• Power surge: press and hold the Test/Reset button for 5 seconds. If it was a surge, the display resets to zero and stays there.
• Sensor error: if the unit goes back to ERR within 5 minutes, it is an actual malfunction. Press and hold Peak Level to show an E-code, then call Kidde at 1-800-880-6788 with the code and the model number, assembly number and manufacture date from the back of the unit.

Kidde calls malfunctions that will not reset, and end-of-life warnings, “non-recoverable” errors: the alarm must be replaced since it will not detect carbon monoxide in these states. If the unit is within warranty, Kidde support can arrange a replacement.

Where To Put A Kidde CO Alarm And How Often To Check It

The CPSC says to install battery-operated CO alarms, or CO alarms with battery backup, on every level of the home and outside sleeping areas. Kidde’s guide says the alarm only senses CO that reaches it, and that if you install just one it belongs near the bedrooms, not in the basement or furnace room. It says not to install the alarm in kitchens, garages or furnace rooms, in spaces colder than 40 F or hotter than 100 F, within 5 feet of heating or cooking appliances (15 feet is recommended), or near vents, flues, fans, doors and windows. Aerosols, paint and solvents can cause temporary readings that are not CO, so move the alarm away first.

For upkeep, the KN-COPP-B-LPM guide says to test the alarm weekly with the Test/Reset button and to vacuum the cover monthly, never using detergents or solvents. Kidde’s replacement page gives a life of 7 to 10 years depending on the model, and the CDC says to replace a detector following the manufacturer’s instructions or every 5 years. The CDC also says to have heating systems and gas, oil or coal appliances serviced by a qualified technician every year.

Frequently Asked Questions

What Does L6 Mean On A Carbon Monoxide Detector?

Kidde lists “Lb” as its low-battery signal on digital CO alarms: a capital L with a lower-case b. Its guide and support pages list no “L6” code, and on a small display the b and the 6 can look alike. A steady number from 30 up with four beeps is a real CO alarm: leave and call 911.

Why Is My Carbon Monoxide Detector Beeping L6?

On the Kidde KN-COPP-B-LPM, a low battery gives one quick beep every 60 seconds with “Lb” on the display, and the fix is to replace all three AA batteries. A beep every 30 seconds is an error, and two beeps every 30 seconds mean end of unit life. Four quick beeps, five seconds of silence and four more is the carbon monoxide alarm.

How Do I Stop My Kidde Carbon Monoxide Alarm From Beeping?

Match the beep to your manual first. For a low-battery chirp, replace the batteries as the manual directs. For an end-of-life or error chirp, new batteries will not stop it and the alarm must be replaced, per Kidde. If the alarm is sounding the four-beep CO pattern, do not try to quiet it: leave the home and call 911.

How Do You Reset A Kidde Carbon Monoxide Detector?

Only reset for the situations Kidde describes. For an ERR message, Kidde says to press and hold Test/Reset for 5 seconds; if the display returns to zero it was a reset, and if it goes back to ERR within 5 minutes the unit has malfunctioned and must be replaced. A low battery has no reset: replace the batteries.

Conclusion

Treat “L6” on a Kidde carbon monoxide alarm as a prompt to read the display and your model’s manual, not as a CO reading. Kidde’s documented low-battery code is “Lb”, a chirp every 60 seconds means low battery, and chirps every 30 seconds mean an error or the end of the alarm’s life. A CO number or the four-beep alarm pattern means leave the home and call 911. For related reading, see our other page on the Kidde carbon monoxide L6 code and our explainer on whether opening a window stops carbon monoxide poisoning.

What this guide does not cover

• Model-specific tables for Kidde combination smoke and CO alarms, hardwired units and plug-in units: use the manual for your model number.