Most smoke detectors do not detect carbon monoxide

A standard smoke detector senses only smoke from fire. It will not alert you to carbon monoxide, which is an odorless, colorless gas that kills without warning. If you need both protections, you must buy a separate carbon monoxide detector or a combination unit that detects both hazards.

The two gases require different sensors. Smoke detectors use optical or ionization chambers to spot particles in the air. Carbon monoxide detectors use electrochemical or biomimetic sensors that react to the gas itself. A device cannot reliably do both jobs with a single sensor, which is why manufacturers either sell them separately or build true dual-function units.

Key Takeaways

  • Standard smoke detectors detect only smoke and will not warn you about carbon monoxide exposure.
  • Combination detectors that sense both smoke and carbon monoxide exist but cost more than buying each separately.
  • Carbon monoxide detectors must be placed on every level of your home and near sleeping areas, separate from smoke detectors.
  • A smoke detector will not replace a carbon monoxide detector, and a carbon monoxide detector will not replace a smoke detector.

How smoke detectors and carbon monoxide detectors work differently

Smoke detectors identify particles suspended in air. An optical smoke detector uses a light beam and a sensor; when smoke enters the chamber, it scatters the light and triggers the alarm. An ionization smoke detector uses a radioactive source to ionize air molecules; smoke disrupts this process and sets off the alarm. Both methods are fast at detecting visible smoke from a fire.

Carbon monoxide detectors sense the gas itself through chemical reaction. An electrochemical sensor contains a chemical solution that reacts when carbon monoxide passes through it, generating an electrical signal. A biomimetic sensor uses a gel that changes color in the presence of carbon monoxide. These sensors are tuned to respond only to carbon monoxide, not to smoke or other gases.

Because the detection methods are completely different, a single device cannot reliably perform both functions. Manufacturers that offer combination units include two separate sensors in one housing, not a single sensor that does double duty.

Combination smoke and carbon monoxide detectors

Combination units exist and are sold under brand names like First Alert and Kidde. They contain both a smoke sensor and a carbon monoxide sensor in one device. The trade-off is cost: a combination detector typically runs $40 to $80, while a basic smoke detector costs $10 to $25 and a basic carbon monoxide detector costs $20 to $50. Buying them separately often costs less unless you need only one or two units total.

Combination detectors are useful in small spaces or when you want to reduce the number of devices on your walls. However, they do not change where you need to place them. You still need smoke detectors in every bedroom and on every level of your home. You still need carbon monoxide detectors on every level and near sleeping areas. A combination unit in your kitchen does not replace a separate smoke detector in your bedroom.

Where to place carbon monoxide detectors in your home

Carbon monoxide detectors should be mounted on every level of your home, including the basement. Place at least one near the bedrooms so you will hear it while sleeping. Additional detectors near fuel-burning appliances — furnaces, water heaters, gas stoves, fireplaces — are recommended but not required by most building codes.

Mount carbon monoxide detectors on a wall at eye level or on a shelf, not on the floor or directly above a heat source. The gas disperses evenly throughout a room, so placement is less critical than with smoke detectors, but keeping it away from direct heat and moisture extends the sensor's life.

Do not place a carbon monoxide detector in the same spot as a smoke detector if you can avoid it. Smoke detectors work best near the ceiling where smoke rises. Carbon monoxide detectors work best at mid-wall height. Separating them ensures each one can do its job without interference.

What carbon monoxide actually is and why you need detection

Carbon monoxide is produced by any fuel-burning appliance: furnaces, water heaters, gas stoves, fireplaces, and car engines. When these appliances work correctly, they vent the gas safely outside. When a vent is blocked, a connection is loose, or an appliance malfunctions, carbon monoxide can leak into your living space.

Breathing carbon monoxide prevents your blood from carrying oxygen. Symptoms include headache, dizziness, weakness, nausea, and confusion — signs that are straightforward to mistake for flu. High exposure can cause loss of consciousness and death within minutes. Because you cannot see, smell, or taste the gas, a detector is your only warning.

The Centers for Disease Control and Prevention reports that unintentional carbon monoxide poisoning kills hundreds of people each year in the United States and sends thousands more to emergency rooms. Most deaths occur in winter when heating systems run constantly and homes are sealed tight. A working carbon monoxide detector can prevent these deaths.

Choosing between separate detectors and combination units

Buy separate detectors if you need many units across your home. The cost per device is lower, and you can choose the best model for each location. A hardwired smoke detector with battery backup in your hallway and a plug-in carbon monoxide detector in your bedroom may serve you better than two combination units.

Buy a combination unit if you need only one or two devices and space is tight. A combination detector in a small apartment or a single-story condo can cover both hazards in one spot, though you should still add a second carbon monoxide detector near your bedroom if the first is far from where you sleep.

Check your local building code before buying. Some jurisdictions require carbon monoxide detectors in all homes; others require them only if you have fuel-burning appliances. Some codes specify hardwired detectors with battery backup for smoke, while others allow battery-only models. Your local fire department or building inspector can tell you what your area requires.

Testing and maintaining both types of detectors

Test your smoke detectors monthly by pressing the test button for three seconds. The alarm should sound loudly. If it does not, replace the battery or the entire unit. Smoke detectors with replaceable batteries need a new battery once a year; hardwired units with backup batteries need the backup battery replaced annually. Replace the entire unit every 10 years.

Test carbon monoxide detectors monthly the same way. Most have a test button that triggers the alarm. If your detector does not have a test button, you cannot verify it is working; replace it with one that does. Replace the battery annually if it uses a replaceable battery. Replace the entire unit every 5 to 7 years, depending on the manufacturer's specifications.

Keep detectors clean and free of dust. Vacuum around them gently or wipe the outside with a dry cloth. Do not paint over them or cover them with anything. Dust and paint can block the sensors and prevent them from detecting smoke or gas.

Frequently Asked Questions

Can I use a carbon monoxide detector instead of a smoke detector?

No. A carbon monoxide detector will not sense smoke from a fire. You need both types of detection. If you want one device, buy a true combination unit that contains both sensors, not a carbon monoxide detector alone.

Do I need a carbon monoxide detector if I have an electric furnace?

No. Electric furnaces, heat pumps, and baseboard heaters do not produce carbon monoxide. You need a carbon monoxide detector only if you have a gas furnace, gas water heater, gas stove, fireplace, or wood-burning stove. If you are unsure what type of heating system you have, ask your landlord or check your utility bills.

What should I do if my carbon monoxide detector goes off?

Leave your home when ready and go outside to fresh air. Call 911 from outside or from a neighbor's home. Do not re-enter until emergency responders have checked the house and cleared it. If the alarm stops but you feel dizzy, weak, or nauseated, seek medical attention and tell the doctor you may have been exposed to carbon monoxide.

Can I install a carbon monoxide detector myself?

Yes. Plug-in detectors and battery-powered detectors require no installation. Hardwired detectors with battery backup should be installed by an electrician if you are not comfortable working with electrical wiring, but many homeowners install them themselves by following the manufacturer's instructions.

How long do carbon monoxide detectors last?

Most carbon monoxide detectors last 5 to 7 years before the sensor degrades. Check the manufacturer's label on your detector for the replacement date. Some detectors will chirp or display a warning when they reach the end of their life. Do not ignore this signal; replace the unit promptly.