How do I know if my smoke alarm detects carbon monoxide?

Author: Kelley Homenick  |  Last update: Wednesday, December 31, 2025

Test for different beeping patterns. Smoke alarms typically sound with 3 beeps in a row, while carbon monoxide detectors usually sound with 4 beeps. Press and hold the button on the front of the detector to test the alarm, and make note of how many beeps it produces.

What will my alarm do if it detects carbon monoxide?

When the carbon monoxide alarm senses a dangerous level of CO gas, the unit will emit a loud alarm pattern. The alarm pattern is four short beeps – followed by five seconds of silence – followed by four short beeps.

How long does it take for a smoke detector to detect carbon monoxide?

The CO alarm sounds if your sensor detects a buildup of carbon monoxide in your home—usually before you start sensing symptoms. With a low CO level (50 ppm), it may take up to eight hours for the alarm to go off. Higher carbon monoxide levels (over 150 ppm) can trigger an alarm within minutes.

What does the red light mean on a smoke detector?

Your alarm manufacturer may have included a blinking red light to let you know it's time to test the alarm again. The Batteries are Low: Usually accompanied by a loud beep, a blinking red light could mean the batteries in the unit are low. Consider adding fresh batteries and running a test to make sure it's working.

Should smoke detectors be red or green?

You will notice two different lights on your smoke alarm: A steady green light shows the alarm is being powered. A red light that flashes once a minute shows the alarm is working.

Understanding Smoke and Carbon Monoxide Detectors | Ask This Old House

Why is the red light blinking on my smoke alarm?

If the red light on your smoke detector is blinking and you're sure there is no fire, change the batteries to stop the blinking. In most cases, this solves the problem. If you change the batteries but the smoke detector continues blinking red, your batteries are likely the culprit.

How do I know if a smoke detector also detects carbon monoxide?

You can purchase each kind of smoke detector or get a dual sensor smoke detector that combines the two methods of detection. Also, some smoke detectors have a CO detector, but you'll need to check the text on the inside of your alarm to see if it does.

What are two warning signs of carbon monoxide poisoning?

The most common symptoms of CO poisoning are headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. CO symptoms are often described as “flu-like.” If you breathe in a lot of CO, it can make you pass out or kill you.

What if the carbon monoxide alarm goes off but no fire?

False or nuisance alarms are when your smoke detector or CO alarm goes off, but there is no presence of smoke or carbon monoxide in your home. However, if your smoke or carbon monoxide detector sounds indicating an emergency and you are not certain it is a nuisance alarm, evacuate the home and call 9-1-1.

Do smoke alarms go off for carbon monoxide?

Fires can produce carbon monoxide, so a smoke alarm won't always detect this gas. On the other hand, carbon monoxide can be present without any visible smoke or flames, making a smoke alarm insufficient for protection.

Will opening a window help with carbon monoxide?

If you experience symptoms that you think could be from CO poisoning: DO GET FRESH AIR IMMEDIATELY. Open doors and windows, turn off combustion appliances and leave the house.

Does the fire department charge to check for carbon monoxide?

In most areas, the fire department does not charge to respond to carbon monoxide alarms or to check for the presence of CO in a residence. However, policies can vary depending on the jurisdiction or specific fire department. It's always a good idea to contact your local fire department for specifics on their policies.

How to know if a fire alarm is going off for carbon monoxide?

In our latest video, we asked the National Fire Protection Association what the noises mean and how to stay safe from fires and carbon monoxide. Here's a simple guide: Smoke alarms alert you with three beeps in a row. Carbon monoxide alarms alert you with four beeps.

How to tell if carbon monoxide is in your house?

It is also a good idea to know the signs of a potential CO problem:
  1. Streaks of soot around fuel-burning appliances, or fallen soot in a fireplace.
  2. Absence of an upward draft in your chimney.
  3. Excess moisture and condensation on windows, walls and cold surfaces.
  4. Rusting on flue pipes or appliance jacks.

What do 5 chirps mean on a smoke detector?

5 Beeps Every Minute: End of Life. This type of chirp indicates it is time to replace your carbon monoxide alarm.

How to test a carbon monoxide alarm?

How to test your carbon monoxide detectors to ensure they are working properly? To test your carbon monoxide detectors, press and hold the test button on the alarm. The detector will sound 4 beeps, a pause, then 4 beeps for 5-6 seconds. Refer to the user manual for your specific model.

What to do if a carbon monoxide alarm goes off and then stops?

If you have a carbon monoxide detector chirping and then it stops, it's important to take the situation seriously, even if the alarm is no longer sounding. Even if the alarm has stopped, get everyone out of the home to a place with fresh air.

How to test for carbon monoxide without a detector?

Any of the following could be a sign of a carbon monoxide leak:
  1. Floppy yellow or orange flame on your gas hob or oven, rather than a crisp blue flame.
  2. Dark, sooty staining on or around gas appliances.
  3. Pilot lights that frequently blow out.
  4. Increased condensation inside windows.

Should I be worried if my smoke alarm goes off for no reason?

Sometimes, smoke detectors will keep going off for no reason when they have reached the end of their life span. Fire alarms have a lifespan of about 10 years, after which they will need to be replaced. Smart smoke detectors can help eliminate some of the annoyances related to false alarms.

How do you know if you have had carbon monoxide poisoning?

A common source is unvented space heaters. Symptoms of CO poisoning include headache, dizziness, weakness, nausea and vomiting, rapid heartbeat, shortness of breath, seizures, chest pain, disorientation, and loss of consciousness.

Why is my smoke detector blinking red?

Most smoke detectors will give a red flashing signal to remind you that the battery needs replacing. Accompanying this, you might hear a chirping sound at regular intervals.

What does a red dot on a smoke detector mean?

The smoke detector battery is low

If your detectors are battery-operated, changing the detector's batteries is the first thing to consider doing when your red light flashes. Most detectors will emit a shrill chirp or beep and a flashing light when they need a battery replacement.

Why is my smoke detector blinking red but no sound?

Here are some examples of why smoke detectors periodically have a flashing red or green LED light without an alarm sounding; To indicate that the alarm is receiving power and is operating normally. An end-of-life or low-battery warning. To indicate the alarm is in hush mode or that there is a fault with the alarm.

Why did my fire alarm randomly go off in the middle of the night?

Why did my fire alarm randomly go off in the middle of the night? This is likely due to one of the common causes like low battery, dirt buildup, humidity, or insects interfering with the sensor. Test the alarm and clean it thoroughly to try and resolve the issue. Make sure batteries are fresh and secure.

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