What is the best way to detect carbon monoxide?

Carbon monoxide (CO) is a poisonous, colorless, odorless, and tasteless gas that can be very dangerous when inhaled. Exposure to high levels of CO can quickly lead to CO poisoning which can result in serious tissue damage, or even death. Having a CO detector in your home is crucial to alert you to rising CO levels so you can take action before CO poisoning occurs. But with different types of CO detectors on the market, how do you choose the right one? Here we’ll compare the most common types of CO detectors, look at the pros and cons of each, and make recommendations for the best CO detectors currently available.

What is carbon monoxide and why is it dangerous?

Carbon monoxide is a combustible gas that is created when fuels like natural gas, propane, gasoline, oil, wood, or coal are burned. Appliances like furnaces, stoves, water heaters, fireplaces, and vehicles produce CO that should vent outdoors through chimneys or exhaust pipes. However, if those vents are blocked or malfunctioning, CO can leak back into indoor spaces.

CO is dangerous because it binds to hemoglobin in the blood more readily than oxygen. When CO is inhaled, it replaces oxygen in the bloodstream and prevents oxygen from reaching organs and tissues. At low concentrations, CO exposure causes fatigue, headaches, dizziness, and nausea. Higher concentrations can result in confusion, unconsciousness, brain damage, and death. Fetuses, infants, elderly people, and those with chronic heart or lung conditions are most susceptible to CO poisoning.

What are the symptoms of CO poisoning?

The most common symptoms of CO poisoning include:

  • Headaches
  • Dizziness
  • Nausea
  • Vomiting
  • Fatigue
  • Weakness
  • Confusion
  • Visual changes
  • Loss of consciousness

However, symptoms can vary widely based on the individual, concentration of CO, and length of exposure. Mild CO poisoning may feel like a cold or flu with no fever. More severe poisoning causes fainting, seizures, or death.

If you suspect CO poisoning, get outside immediately to fresh air and call emergency services. CO exposure can cause long-term neurological issues so it’s crucial to get medical attention even if you feel fine after getting fresh air.

Where does CO come from in the home?

There are many potential sources of CO inside a home, including:

  • Gas or oil furnaces and boilers
  • Gas water heaters
  • Gas stoves and ovens
  • Gas dryers
  • Fireplaces and wood stoves
  • Gas or charcoal grills used indoors
  • Generators and other gasoline-powered equipment used indoors or near air intakes
  • Tobacco smoke
  • Attached garages with car engine exhaust leaking indoors

Faulty chimneys or flues, blocked vents, cracked heat exchangers, and other appliance issues can all cause CO to leak into the home. Using combustion appliances without proper ventilation is a common cause of CO poisoning.

Where should you have CO detectors in your home?

Experts recommend installing CO detectors:

  • On every level of the home
  • Near all sleeping areas
  • Near combustion appliances like furnaces, hot water heaters, and fireplaces
  • In common areas where people spend time like living rooms

Having detectors at breathing level (about 5 ft from the floor) increases their effectiveness. Additional detectors near bedrooms or on upper/lower levels of the home provide extra protection.

For the most comprehensive coverage, install CO detectors on every level, in every bedroom, and in common spaces. Units that plug into outlets work well in bedrooms while battery-powered or hardwired detectors suit other central locations.

What are the different types of CO detectors?

There are 3 main types of CO detectors:

Battery-powered CO detectors

Battery-powered detectors, also called portable detectors, run solely on self-contained batteries. They can easily be placed anywhere in the home. Since they don’t require wiring, battery-powered units can be moved around and used for travel or temporary situations. However, the batteries must be replaced every 6 months to 2 years. They’re more prone to failure if batteries are not changed regularly.

Plug-in CO detectors

Plug-in CO detectors plug directly into a standard electrical outlet. They can be installed anywhere an outlet is available. Since they’re powered by electricity, they don’t require battery changes. However, plug-in models don’t work if the power goes out. They can also be unplugged accidentally. Some plug-in detectors have battery backup for use during power outages.

Hardwired/interconnected CO detectors

Hardwired detectors connect directly to the home’s electrical system and don’t need batteries or charging. They can be either stand-alone detectors or interconnected units. Interconnected hardwired detectors have backup battery power and work together so if one alerts, they all sound the alarm. Hardwired detectors work even during power outages. However, they require professional installation and are not portable.

How do the different types of CO detectors work?

CO detectors use different types of sensors to test for CO in the air:

  • Biomimetic sensors contain a gel that mimics the reaction of hemoglobin to CO. When CO is present, it changes the gel’s color or conductivity, triggering an alarm.
  • Metal oxide semiconductor sensors detect CO with an electrically heated wire coated in tin dioxide. CO interacts with the coating, changing the wire’s resistance and sounding the alarm.
  • Electrochemical sensors use a chemical reaction between CO and the sensor to detect CO and trigger an alarm.
  • Infrared sensors measure how much infrared light is absorbed by CO molecules in the chamber.

While all sensor types can effectively detect CO, electrochemical and biomimetic sensors last longer (5-10 years) compared to metal oxide semiconductor (2-3 years) and infrared (5-6 years) sensors before they must be replaced.

What features should you look for in a CO detector?

Key features to seek in an effective CO detector include:

  • ANSI/UL certification – Verify the detector meets safety standards for CO detection.
  • Sensor type – Electrochemical and biomimetic sensors last the longest.
  • Detection levels – Look for a low-level alarm at 30 ppm and high alarm at 100-150 ppm.
  • Digital display – Displays current CO levels detected for awareness.
  • Warranty – 5-10 year warranties are ideal for the detector’s lifespan.
  • Audible alarm – At least 85 dB loud to notify of high CO.
  • Testing/silence button – For monthly tests and to temporarily silence low battery alarms.

Additional useful extras include interconnectivity between hardwired detectors, battery backup, memory to record CO levels, and connection to smart home systems.

Where should you avoid placing CO detectors?

Avoid installing CO detectors in the following locations:

  • Near appliances or areas where CO may occur like furnaces, stoves, and fireplaces (install at least 15 feet away)
  • In excessively humid, cold, or hot spots
  • Near vents, doors, windows, or anywhere drafts occur
  • In dead air spaces like corners or behind furniture
  • In dusty or dirty areas
  • Near chemicals or cleaners that could damage the sensors
  • In insect-infested areas
  • Near very loud noise sources like speakers or TVs
  • In garages, kitchens, crawlspaces, unfinished attics, or bathrooms

Placing detectors incorrectly reduces their effectiveness at detecting CO leaks. Optimal locations are in open central areas of living spaces.

How much do CO detectors cost?

Basic battery-powered CO detectors range from $20-$50. Units with digital displays, 10-year sealed batteries, and more sensors cost $50-$100. Hardwired and plug-in detectors cost $40-$80.

Smart detectors with wifi connectivity, mobile apps, and voice control integration are $80-$250. Low-cost CO detectors under $20 are not recommended, as they may be less accurate and durable.

Buying multiple detectors provides better coverage than a single unit. Prices per detector decrease when purchasing value packs of 3-4 units. Overall costs are lowest for battery-powered units, followed by plug-in and hardwired.

Here are typical price ranges for each type:

  • Battery-powered – $20-$100 per unit
  • Plug-in – $40-$80 per unit
  • Hardwired – $50-$150 per unit
  • Smart detectors – $80-$250 per unit

Consider spending more for detectors with long-lasting sensors, better warranties, and extra features like displays and connectivity. This provides more accurate and consistent CO detection.

What’s the difference between CO alarms and CO detectors?

The terms “carbon monoxide alarm” and “carbon monoxide detector” are often used interchangeably, but they refer to slightly different devices:

CO alarms both detect CO and sound an audible alarm when elevated CO is detected. CO alarms include battery-powered, plug-in, and hardwired detectors with built-in alarm sounds.

CO detectors sense CO but do not emit an audible alarm sound themselves. Instead they communicate wirelessly with a control panel that triggers the audible alarm. Detectors only have the detection function while the control unit alarms.

However, many models called “CO detectors” also include alarm abilities. So in practice, CO alarms and detectors have nearly identical functionality. Both terms refer to devices that both sense CO levels AND sound an alarm when unsafe conditions are detected.

How do you test a CO detector?

CO detectors should be tested monthly to verify they are working correctly. There are two ways to test them:

Push-button test – Many detectors have a test/silence button on the cover. Press and hold the button for a few seconds until the alarm sounds, then release. This tests the detector’s alarm sound and battery power.

Aerosol CO spray – Special aerosol sprays contain CO that simulates real CO when released. Spray a short burst near the detector then wait for the alarm. CO test sprays provide a more realistic test.

After testing, reset the detector if needed so it’s no longer in alarm mode. If no alarm sounds during a test, the batteries or detector may need replacing. Always refer to manufacturer instructions for proper testing methods.

What should you do if your CO detector goes off?

If your CO detector activates its alarm, follow these steps immediately:

  1. Evacuate everyone from the home and move outside to fresh air.
  2. Call 911 to report suspected CO poisoning and request emergency assistance.
  3. Open windows and doors to ventilate and remove CO from the home.
  4. Turn off any appliances that may be releasing CO, if it’s safe to re-enter the home.
  5. Do not reenter the home until emergency responders say it is safe.

The most important step is to get outside to protect yourself and others from CO exposure. Even if you think it may be a false alarm, take appropriate precautions. Do not ignore the alarm.

How can you prevent CO leaks in your home?

You can help prevent hazardous CO situations by taking these precautions:

  • Install UL-listed CO detectors throughout the home according to manufacturer guidelines.
  • Have all fuel-burning appliances inspected annually by professional HVAC contractors.
  • Ensure appliances are properly vented outside.
  • Never run generators, grills, or other gas-powered machines indoors or in garages.
  • Clear blockages and soot buildup from chimneys, vents, and flues.
  • Open the fresh air supply on high-efficiency furnaces and water heaters.
  • Hire a CSIA-certified chimney sweep if using wood-burning fireplaces.
  • Never idle cars in attached garages, even with the garage door open.
  • Install window/door alarms to alert you if they’re accidentally left open.

Taking preventative measures greatly reduces the chances of CO leaks. But CO detectors provide an extra layer of protection in case any issues arise.


Carbon monoxide is a toxic gas that you can’t see, smell, or taste, making detectors absolutely essential. While all CO detector types effectively monitor CO levels, battery-powered detectors offer flexibility in placement, plug-in models provide continuous power, and interconnected hardwired systems maximize whole-home coverage. Electrochemical and biomimetic sensor detectors last the longest, around 5-10 years. Look for key features like ANSI/UL certification, digital displays, and 85+ dB alarms. Strategically place detectors to avoid device-killing conditions like humidity, dust, and dead air spaces. Overall, the combination of properly installed long-lasting CO detectors, proper appliance maintenance, and safe usage of combustion devices offers the best protection against dangerous CO leaks in the home.

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