Last Updated June 2026

No — a standard smoke detector cannot detect carbon monoxide. And a standard CO detector cannot detect smoke. Smoke alarms and CO detectors operate differently, and their sensors are designed to detect different threats.

The National Fire Protection Association recommends having both smoke and CO protection in the home — either as separate units or as combination alarms that are designed to detect both.

If you see a detector labeled “smoke alarm” only, don’t assume it covers CO — and vice versa. The label and product specifications will tell you exactly what it’s designed to detect.

Labels on combination alarms list Underwriters Laboratories (UL) numbers for both kinds of sensors: UL 217 (for smoke) and UL 2034 (for CO). The device should specifically list that it is a combination unit.

Installing each type of device in the right place matters, and so does replacing batteries or the device itself at scheduled times. Separate devices may allow for more flexibility in placement. A combination alarm can be a practical option where space or outlets are limited, as long as it’s a certified combo unit.

Quick answer: Smoke vs. CO detection

• Standard smoke alarms: detect smoke, not CO
• CO detectors: detect carbon monoxide, not smoke
• Combination alarms: detect both, but only if they are UL rated for both functions

What is the difference between smoke and carbon monoxide?

Smoke is produced when materials burn. You can see it and smell it. It rises quickly, which is why smoke detectors are typically mounted high on walls or on ceilings. Inhaling smoke can irritate the airways, cause respiratory problems and, in serious fires, be life-threatening.

Carbon monoxide (CO) is a very different byproduct of burning. You can’t see it or smell it. It’s a gas produced when carbon-based fuels like natural gas, propane, oil, wood or coal don’t burn completely. Common household sources include gas furnaces, gas water heaters, fireplaces, portable generators used indoors and attached garages where cars and other gas-burning equipment are housed. Because it’s colorless and odorless, people can breathe it in without knowing it. Even low levels can cause headaches, dizziness, nausea and confusion. At higher concentrations, CO exposure can be fatal.

Because smoke and CO are so different, they require different types of detectors.

What is a smoke detector?

A smoke detector monitors household air for particles produced by something burning. The two main types operate differently.

• Ionization smoke alarms use a small amount of radioactive material to ionize the air inside a sensing chamber. When smoke enters the chamber, it disrupts the electrical current and triggers the alarm. Ionization alarms tend to respond quickly to fast-burning fires.
• Photoelectric smoke alarms use a light source and a sensor. When smoke scatters the light beam, the sensor detects the change and sounds the alarm. Photoelectric alarms often respond earlier to slow, smoldering fires.

Some smoke detectors combine the two technologies. The National Fire Protection Association (NFPA) recommends that every home have smoke alarms inside each bedroom, outside sleeping areas and on every level of the home, including the basement. It also recommends testing smoke detectors every month, replacing batteries yearly (newer models have lithium batteries designed to last 10 years) and replacing them every 10 years.

Learn more about fire prevention and about how smoke alarm safety can make a difference.

What is a carbon monoxide detector?

A CO detector continuously samples household air for carbon monoxide. When CO levels reach a threshold that can be harmful, the alarm sounds. They use a few types of sensors.

• Electrochemical CO sensors. The most common type in residential detectors, these use a chemical reaction to measure CO levels and are known for accuracy.
• Biomimetic CO sensors. A gel changes color when it absorbs CO, triggering the alarm.
• Metal oxide semiconductor sensors. A sensor chip detects CO and reduces electrical resistance when exposed to the gas.

The Consumer Product Safety Commission (CPSC) recommends installing CO detectors on every level of the home, especially near sleeping areas. Placement typically is near the floor, since CO disperses fairly evenly in a room, but check your device’s installation guide.

According to the CPSC, carbon monoxide detectors should be tested regularly, batteries changed once a year (newer models have lithium batteries designed to last 10 years) and replaced every five to seven years, or per the manufacturer’s instructions.

At a glance: Smoke alarm vs. CO detector vs. combination alarm

A note on safety

If your CO detector goes off, don’t ignore it. Get everyone outside immediately, call 911 from outdoors and don’t re-enter the home until emergency responders say it’s safe. If anyone in the home experiences a headache, dizziness, nausea or confusion and you suspect CO exposure, treat it as an emergency.

For questions about installation, contact a licensed electrician or your local fire department.

Smoke and carbon monoxide detectors can help alert you to danger early, and the right home insurance coverage can help you prepare for the unexpected if damage occurs.

The information contained in this page is provided for general informational purposes only. Read our editorial standards for Insurance Questions and other content. We make no representations or warranties of any kind, express or implied. This does not refer to any specific insurance policy and nothing herein is intended to replace or modify any terms in your actual policy.

Farmers may also provide information on topics that are not directly about insurance policies or coverage that we believe could be helpful to you. Information in such articles is not meant as professional advice, and any reliance you place on such information is therefore strictly at your own risk.

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