What Does a Carbon Monoxide Detector Do and How Does it Work?

It might seem like a time-saver to run your car in the garage before a long commute, especially on a cold winter’s morning. But the emissions from your vehicle can fill your garage with carbon monoxide (CO)—a dangerous, silent threat—even if the garage door is open.

Carbon monoxide is a colorless, odorless, and poisonous gas that claims over 430 lives a year.¹

It’s a byproduct of burning carbon fuel like the natural gas in your stove and the gasoline in your car. Even small doses of carbon monoxide can cause permanent damage or death.

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Carbon monoxide gas (CO gas) is a simple molecule: one part carbon and one part oxygen. Carbon monoxide comes when carbon fuel—like wood, gasoline, coal, propane, natural gas, and heating oil—fails to burn completely (incomplete combustion).

These energy sources aren’t dangerous when you burn them in an open area with plenty of ventilation. But carbon monoxide is hazardous in confined spaces—like basements, kitchens, garages, or campers.

Carbon monoxide is hard to detect without a sensor, which is one of the reasons it’s so dangerous.

There are several common sources of carbon monoxide gas:

• Fuel-burning appliances like heating systems or water heaters
• Consumer products like grills
• Engine-driven tools like generators

Carbon monoxide is deadly because it binds with your red blood cells and starves your body of oxygen after passing into your lungs.

These are the early symptoms of carbon monoxide poisoning:

• Headache
• Nausea
• Vomiting
• Dizziness
• Shortness of breath
• Fatigue

Perhaps most troubling is the similarity to cold or flu-like symptoms that are easy to ignore—shortness of breath, nausea, and mild headaches. Disorientation and unconsciousness can occur when levels of carbon monoxide reach 150 parts per million (ppm).² Eventually, the symptoms turn lethal without treatment.

Carbon monoxide poisoning is a serious risk, but fortunately, it’s preventable. Stop CO sources and be prepared.

Here are five carbon monoxide safety tips for avoiding exposure, including installing CO sensors throughout your home:

• Never heat your home with a gas range. Gas stoves produce carbon monoxide and can fill your home with dangerous gas.
• Don’t run your car in the garage. Pull out of the garage first if you want to warm up your vehicle in the winter. Carbon monoxide is a common byproduct of vehicle exhaust and builds up quickly in a closed (or even open) garage.
• Always have proper ventilation. It’s extremely dangerous to run gas-powered tools (like generators, space heaters, and pressure washers) in an enclosed area like a basement or garage without adequate ventilation.
• Practice cooking safety while camping. You should enjoy the wilderness safely. Don’t use a charcoal grill, hibachi, or camping stove inside your home, tent, or camper. Besides, open flames and fabric tents don’t tend to get along.
• Install a carbon monoxide detector. The best carbon monoxide detectors are affordable, easy to install, and can save your life. We recommend installing one on every level of your home, near each bedroom and garage, to test the air quality.

Carbon monoxide detectors sound an alarm when they sense a certain amount of carbon monoxide over time. Different sensors set off different types of alerts:

• Biomimetic sensor: a gel changes color when it absorbs carbon monoxide, and this color change triggers the alarm.
• Metal oxide semiconductor: when the silica chip’s circuitry detects carbon monoxide, it lowers the electrical resistance, and this change triggers the alarm.
• Electrochemical sensor: electrodes in a chemical solution sense changes in electrical currents when they come into contact with carbon monoxide, and this change triggers the alarm.

Once the carbon monoxide detector alarm sounds, it must be in a carbon monoxide-free environment to silence the siren.

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.³

Act quickly when an alarm sounds because low doses over long periods can be just as dangerous as sudden carbon monoxide exposure in ultra-high doses.

1. First, don’t panic. Gather everyone in your house and move outside for fresh air and to avoid further CO exposure.
   • On the way outside, open as many doors and windows as possible to help air out your home. To reduce exposure, don’t go out of your way to open every door and window, just the ones along the way.
   • Know the difference between an actual alarm and the detector's "end of life" alarm, which has a different sound.
2. Survey everyone’s health and check for any flu-like symptoms that could suggest poisoning.
3. If you notice any symptoms, call 911 immediately.
4. If possible, do not reenter your home until the alarm stops sounding or emergency responders deem your home safe.
5. Contact a professional to evaluate every fossil fuel-burning appliance (particularly furnaces, boilers, water heaters, and stoves) and any other possible source of carbon monoxide to prevent a future incident.

Regular maintenance and inspections can help prevent safety hazards in your home, like a faulty furnace or fireplace.

Overall, carbon monoxide detectors sense CO fast and alert you as soon as they do. But there’s a surprising amount of variety in today’s carbon monoxide sensors.

Some simple models plug into outlets or use a battery and alert you with a loud siren, like the one on your smoke detector. These models are cheap and suitable for multi-room buildings that need several units spread throughout.

Many models include sensors for both smoke and carbon monoxide. These are easy options you can swap out your existing smoke detectors for. They also reduce the number of sensors on your walls or ceilings.

You can also find smart models that connect with your home security system or alert you of danger through a mobile app. These models are expensive but can be a wise investment if you want extra safety for kids and pets at home.

You can learn more about CO detectors and how they work in our FAQ guide.

Ensure everyone in the house can hear when an alarm goes off by placing a CO sensor in or near each of three critical locations in your home:

• At least one on each level—including the basement and attic
• Near each bedroom or sleeping space
• By doors that lead to attached garages

Follow your local laws and the manufacturer’s instructions for additional guidance beyond these three locations (for example, some states require sensors in utility rooms). For more information, you can also check out our guide on the best places to install CO monitors.

First, find out if your local laws require carbon monoxide detectors inside every enclosed sleeping area in a dwelling unit. In these cases, you need a sensor for every bedroom.

Most states require sensors within a certain distance of bedrooms, so a single sensor in a shared hallway can cover multiple bedrooms. This overlaps with the “one-sensor-per-level” rule.

Check out our best carbon monoxide detectors buyers guide to find one that fits your needs.

• The Best Carbon Monoxide (CO) Detectors
• What Does a Carbon Monoxide Detector Do and How Does it Work?
• Where Should I Install CO Monitors?
• Best Fire and Smoke Alarms for the Home
• How to Detect a Gas Leak in Your Home

1. Centers for Disease Control and Prevention, "Carbon Monoxide Poisoning (CO)," March 23, 2022. Accessed July 29, 2022.
2. United States Consumer Product Safety Commission, "Carbon Monoxide Questions and Answers." Accessed July 29, 2022.
3. Kidde, Fire Safety, "What Are the Carbon Monoxide Levels That Will Sound the Alarm?," October 2019. Accessed July 29, 2022.
4. National Fire Protection Association, "Carbon Monoxide Alarms." Accessed July 29, 2022.