Smoke or CO alarm beeping, chirping or flashing? What it means, by brand
63 signals from 7 makers’ own manuals. One chirp a minute is a low battery on one make and a failed sensor on another, so pick what you see or hear.
A loud, continuous alarm is not a fault. All 7 makers give the same first step: get out, and call the fire service. Each maker’s own words.
Find it by what you see or hear
63 signals.
- Kidde: Loud pulsing alarm that does not stopReal alarm
- Kidde: Four short beeps, five seconds of silence, repeatingReal alarm
- Kidde: One chirp every 30 to 40 secondsLow battery
- Kidde: Chirp between flashes of the red LEDFault
- Kidde: Chirp every 30 to 40 seconds for about seven minutes after you pressed HushHush or silence mode
- Kidde: Chirp every 30 seconds on a sealed-battery alarmEnd of life
- Kidde: CO alarm chirping every 30 secondsEnd of life
- Kidde: CO alarm chirping once every 60 secondsLow battery
- Kidde: CO alarm display showing a numberReal alarm
- Kidde: “Lb” on a CO alarm displayLow battery
- Kidde: Green light on a Kidde smart alarmNormal operation
- Kidde: Amber light on a Kidde smart alarmFault
- First Alert: Green flash once a minute, no soundNormal operation
- First Alert: Three beeps, pause, repeating, red LED flashing, escape light onReal alarm
- First Alert: Silent, red LED three flashes and a pause, escape light onHush or silence mode
- First Alert: Three chirps every minute, three green flashesFault
- First Alert: Five chirps every minute, one green flashLow battery
- First Alert: Five chirps every minute, five green flashesEnd of life
- First Alert: Green LED flashing twice a minute, no soundFault
- FireAngel: One red flash about every 40 seconds, no soundNormal operation
- FireAngel: Loud alarm, red LED flashing once a secondReal alarm
- FireAngel: Quiet after pressing Test, LED still flashing once a secondHush or silence mode
- FireAngel: One beep and one flash every 40 secondsLow battery
- FireAngel: A double beep and a double flash every 40 secondsFault
- FireAngel: A triple beep and a triple flash every 40 secondsEnd of life
- FireAngel: Four loud beeps and a pause, repeating (CO alarm)Real alarm
- FireAngel: CO alarm flashing red every 20 seconds, silentAlarm memory
- FireAngel: Three rapid beeps and three yellow flashes every 60 seconds (FA6829S)End of life
- Aico: Full alarm sound, red light flashing rapidlyReal alarm
- Aico: Silent, red light flashing every 8 to 10 secondsHush or silence mode
- Aico: One beep about every 32 seconds with a red or yellow flash at the same timeLow battery
- Aico: Two beeps every 32 seconds with two flashesFault
- Aico: Red light flashing twice every 16 seconds, silent (Ei650i)Alarm memory
- Aico: Regular single beep about once a minute (mains alarm)Low battery
- Aico: Irregular beep with no pattern (mains alarm)Fault
- Aico: CO alarm soundingReal alarm
- Google Nest Protect: Pulsing red ring, alarm, “Emergency. There’s smoke in the (room)”Real alarm
- Google Nest Protect: Pulsing red ring, alarm, “Emergency. There’s carbon monoxide…”Real alarm
- Google Nest Protect: Pulsing yellow ring, “Heads-Up. There’s smoke in the (room)”Early warning
- Google Nest Protect: Pulsing yellow ring, “Heads-Up. There’s carbon monoxide…”Early warning
- Google Nest Protect: Pulsing ring and “Smoke (or carbon monoxide) alarm silenced”Hush or silence mode
- Google Nest Protect: Pulsing green ring, “The smoke alarm is over in the (room)”Normal operation
- Google Nest Protect: Brief green glow when you turn the lights offNormal operation
- Google Nest Protect: Yellow ring, “The batteries are low… Replace the batteries soon”Low battery
- Google Nest Protect: One chirp every 60 seconds, “The batteries are very low”Low battery
- Google Nest Protect: One chirp every 60 seconds, “The sensors have failed… Replace Nest Protect now”Fault
- Google Nest Protect: Two chirps every 60 seconds, “Nest Protect has expired”End of life
- Google Nest Protect: Yellow ring, “Nest Protect is offline”Fault
- Google Nest Protect: Pulsing blue ring, “Hi” or “Press to test”Normal operation
- X-Sense: One red flash every 60 seconds, no soundNormal operation
- X-Sense: Short quick beeps, red LED flashing once a secondReal alarm
- X-Sense: Silent, red LED flashing once every 5 secondsHush or silence mode
- X-Sense: One beep and one red flash every 60 secondsLow battery
- X-Sense: Two beeps and two red flashes every 40 secondsFault
- Ei Electronics: Continuous alarm, red light flashing rapidlyReal alarm
- Ei Electronics: Three long beeps and a pause, repeating, red LED flashingReal alarm
- Ei Electronics: CO alarm flashing red two, three or four times every 4 secondsEarly warning
- Ei Electronics: One chirp and one yellow flash every 48 secondsLow battery
- Ei Electronics: Two chirps and two yellow flashes every 48 secondsFault
- Ei Electronics: Three beeps and three yellow flashes every 48 secondsEnd of life
- Ei Electronics: Four beeps and four yellow flashes every 8 secondsFault
- Ei Electronics: One beep with a red flash every 40 seconds (140e series)Low battery
- Ei Electronics: Green power light off, regular single beepFault
No signal matches all of those. Try “Any” on one of the choices: makers describe the same pattern in different ways (a beep on one is a chirp on another).
If it sounds: each maker’s own words
The first step each maker gives for a sounding smoke alarm, in its own words. Each brand page has the whole instruction, and the carbon monoxide one:
- Kidde: check for fire, then leave at once by your escape plan and call the fire department from a neighbour’s house.
- First Alert: get everyone out of the house immediately, then call the fire department from outside.
- FireAngel: if you are not absolutely certain of the source, get everyone out immediately and call the fire and rescue service (999).
- Aico: evacuate — if in doubt, assume the fire is real — and call the Fire Brigade from a neighbour’s house or a mobile.
- Google Nest Protect: at “Emergency”, get out of the house immediately, then call the fire department.
- X-Sense: if you see or smell smoke, evacuate immediately and call emergency services.
- Ei Electronics: if in doubt assume the fire is real: get out as fast as you can and call the Fire Brigade immediately.
The same chirp, different meanings
Chirp patterns that at least two makers use for different things. This is why no single chart of beeps is right for every alarm.
| You hear | What it means, by brand |
|---|---|
| One chirp, about every 20–45 seconds |
|
| One chirp, about every 48–60 seconds |
|
| Three chirps, about every 48–60 seconds |
|
| Two chirps, about every 48–60 seconds |
|
By brand
What these pages cannot do
- They cannot identify your model. Each page names the manual or support page it comes from; a model outside it may use other signals.
- They never say a signal is safe to leave. End of life means the maker’s instruction to replace the alarm; a fault means the maker’s fix or a replacement.
- They do not replace a real alarm response: a loud continuous alarm is the maker telling you to get out.
Left out, and why
Every brand on the list had at least 5 states documented on its own site, and none refused the fetch. These parts were left out:
- First Alert support articles — support.firstalert.com/s/article/… pages (e.g. “What do the chirps mean”, “SC5 LED colors explained”) return only a script shell to a plain fetch, with no article text. We used the SM210L user’s manual PDF from the same First Alert host instead, so First Alert’s CO and smart (SC5) alarms are not covered yet.
- First Alert and X-Sense CO alarms — No CO or combination manual from either maker was read for this page, so neither brand has a CO page; their smoke pages say they cover smoke only.
- X-Sense XS01 (ETL edition) manual — The PDF on download.x-sense.com stores its text as drawn outlines, so it could not be read and quoted. The XS01-WR manual, which could, is used instead.
- Kidde model manuals and ERR codes — Kidde’s support pages cover its range as a whole; the ERR codes of Kidde’s digital CO alarms differ by model and are left to each model’s manual.
- Aico 3000 series indicator table — The Ei3014/Ei3016/Ei3024 manual on aico.co.uk lays its indicator table out so that the text comes out scrambled; the 3000 series patterns are taken from Ei Electronics’ own FAQ instead (the Ei Electronics pages).
Sources
Each brand’s own manuals and support pages only, read on the date shown.
Kidde
- Kidde: What Causes Consistent Chirping? — Kidde smoke and CO alarms, US range (support article; no single model). www.kidde.com Checked 2026-09-29.
- Kidde: What is Causing My Smoke Alarm to Sound, Beep, or Chirp? — Kidde smoke alarms, US range (support article). www.kidde.com Checked 2026-09-29.
- Kidde: What to Do When Your Smoke Alarm Sounds — Kidde smoke alarms, US range (support article). www.kidde.com Checked 2026-09-29.
- Kidde: What Should I Do When My Carbon Monoxide Alarm Sounds? — Kidde CO and combination alarms, US range (support article). www.kidde.com Checked 2026-09-29.
- Kidde: Why Is My Carbon Monoxide Alarm Beeping or Chirping? — Kidde CO alarms, US range (support article). www.kidde.com Checked 2026-09-29.
- Kidde: What do the different LED colors mean on my Smart smoke device? — Kidde smart smoke and smoke + CO alarms (support article). kidde.com Checked 2026-09-29.
- Kidde: What Causes Intermittent Beeping or Chirping? — Kidde smoke, CO and combination alarms, US range (support article). www.kidde.com Checked 2026-09-29.
First Alert
- First Alert (BRK Brands): User’s Manual — Smoke Alarm, 10-Year Sealed Battery with Escape Light — Model SM210L. support.firstalert.com Checked 2026-09-29.
- First Alert: Why Is My Smoke Detector Beeping (Safety Corner) — First Alert smoke alarms (general article). www.firstalert.com Checked 2026-09-29.
FireAngel
- FireAngel Safety Technology: FA6611, FA6615 & FA6620 Optical Smoke Alarm & FA6720 Heat Alarm — User Manual — FA6611, FA6615, FA6620, FA6720 (document GN5914R3). www.fireangel.co.uk Checked 2026-09-29.
- FireAngel Safety Technology: Why is my FireAngel CO alarm beeping and flashing? — FA3313 and FA3820 CO alarms (support article). www.fireangel.co.uk Checked 2026-09-29.
- FireAngel Safety Technology: Fire & Smoke Alarm FAQs — FA6615-R, FA6620-R, FA6829S, FA3820-EUX10 (FAQ entries). www.fireangel.co.uk Checked 2026-09-29.
- FireAngel Safety Technology: Why is my FireAngel smoke alarm beeping? — FireAngel smoke and heat alarms (support article). www.fireangel.co.uk Checked 2026-09-29.
Aico
- Aico: Homeowner FAQs — Why is my alarm beeping? — Aico mains and CO alarms, incl. 140RC series (FAQ). www.aico.co.uk Checked 2026-09-29.
- Aico / Ei Electronics: Battery Powered Smoke Alarms Ei650 Series — instruction leaflet (Rev 6) — Ei650, Ei650C, Ei650W, Ei650i. www.aico.co.uk Checked 2026-09-29.
- Aico: Basic Alarm Fault Finding — Aico alarms (trade fault-finding page). www.aico.co.uk Checked 2026-09-29.
Google Nest Protect
- Google: Nest Protect lights and sounds — Google Nest Help — Nest Protect (1st and 2nd gen, battery and wired). support.google.com Checked 2026-09-29.
- Google: What to do if Nest Protect detects smoke in your home — Google Nest Help — Nest Protect. support.google.com Checked 2026-09-29.
X-Sense
- X-Sense: Wireless Interlinked Smoke Alarm XS01-WR — User Manual — XS01-WR (UL 217 edition). download.x-sense.com Checked 2026-09-29.
- X-Sense: Smoke Detector Beeps and Sounds Decoded — X-Sense smoke alarms (general guide). www.x-sense.com Checked 2026-09-29.
Ei Electronics
- Ei Electronics: Products FAQs — Why is my fire alarm beeping? / Why is my alarm beeping? — Ei 3000 series, 600 series, 140e series and CO alarms (FAQ). www.eielectronics.ie Checked 2026-09-29.
- Ei Electronics: Ei3028 / 3018 Alarms Instruction Manual — Ei3028 multi-sensor heat and CO alarm, Ei3018 CO alarm (document B20223 R5, Irish edition). www.eielectronics.ie Checked 2026-09-29.
- Ei Electronics: Basic Alarm Fault Finding — Ei alarms (fault-finding page). www.eielectronics.ie Checked 2026-09-29.