A carbon monoxide (CO) alarm has a very distinct emergency sound: it’s usually four loud beeps (or chirps) in a row, followed by a short pause, repeating over and over until the danger is gone or the alarm is silenced.

What a carbon monoxide alarm sounds like

Most modern CO alarms follow a similar pattern so you can tell them apart from smoke alarms.

  • Four short, loud beeps, then a pause, repeating (often written as “beep-beep-beep-beep – pause”).
  • The beeps are high-pitched and urgent, designed to wake you up from sleep.
  • Some models also speak, saying something like “Warning: carbon monoxide” along with the beeps.

By contrast, many smoke alarms use three beeps in a row instead of four, so counting the beeps helps you know which danger you’re facing.

Other sounds your CO alarm can make

Your CO alarm doesn’t only warn about gas; it also tells you about its own health.

  • 4 beeps + pause, repeating: Emergency – dangerous CO level detected; treat this as life-threatening.
  • 1 short chirp every 30–60 seconds: Low battery; replace the batteries as soon as possible.
  • 5 short chirps every minute (or a different repeated pattern): End-of-life for the unit; you need a new alarm.

Check the manual or the label on your specific model, since patterns can vary slightly between brands.

What to do if it’s the 4‑beep alarm

If you hear the full four-beep emergency pattern:

  1. Leave the building immediately and get into fresh air.
  1. Call emergency services (such as 911) from outside or from a neighbor’s place.
  1. Do not go back inside until professionals say it’s safe; CO is invisible and odorless, so you can’t judge it yourself.

A simple way to remember:

Three beeps = smoke,
Four beeps = carbon monoxide.

Information gathered from public forums or data available on the internet and portrayed here.