What Do Carbon Monoxide Detectors Do and How Do They Work?

Of all the household dangers that can kill you, few are as unsettling as carbon monoxide.

It’s been compared to an invisible, venomous snake moving through your home undetected, but that analogy undersells it. Unlike lead paint, which at least has a physical presence, carbon monoxide gives you nothing. No smell, no color, no taste. Just a gas that can kill you quickly, sometimes within minutes.

That’s why CO detectors are essential in every home and why most states require them to pass building codes. They detect the gas before the worst symptoms of exposure set in, and in doing so, they save lives. Read on for a closer look at what good CO detectors do and how they work. And since many CO emergencies happen during colder months, it’s worth pairing this with our guide to winter home safety.

Let’s take a deep dive into what good CO detectors do and how they work, so you can keep one ugly, invisible killer out of your home. While you’re at it, read our guide to winter home safety, because many CO emergencies happen during colder months.

Know Your Enemy: Understanding Carbon Monoxide and Carbon Monoxide Poisoning

Carbon monoxide is a colorless, odorless gas produced by burning fuel. Most household appliances and engines that rely on combustion generate it, and when ventilation is poor or equipment isn’t functioning correctly, it can seep out through vents and flues. Common culprits include gas stoves, fireplaces, furnaces, vehicles, and portable generators.

Poisoning occurs when CO accumulates in the bloodstream faster than the body can clear it. The problem is biological: CO binds to hemoglobin far more readily than oxygen does, which means the body effectively trades one for the other. As exposure continues, oxygen gets crowded out, leading to tissue damage and, in severe cases, death.1

It’s not pretty. The gas affects the brain and heart the most, so symptoms can feel similar to having the flu:

• Nausea
• Headache
• Dizziness
• Blurred vision
• Loss of muscle control and consciousness

People can even experience dangerous symptoms after recovering from major CO poisoning:

• Movement issues
• Changes in personality
• Brain fog and memory loss

CO earned its nickname, the Silent Killer, for good reason. It’s a serious hidden household danger, but the kind every homeowner can stop with one fairly simple device. Enter the CO detector.

Know Your Guardian: Carbon Monoxide Detectors

CO detectors are compact devices that mount easily to walls or ceilings. Round models typically run 4 to 6 inches in diameter, while square ones land somewhere between 3 and 5 inches across.

Their job is to measure how much carbon monoxide has accumulated in a given space and trigger an alarm before concentrations reach dangerous levels. Most models measure in parts per million, and while alarm thresholds vary by device, the better ones are sensitive enough to catch low concentrations early, giving people time to respond before symptoms set in.

The three most common sensor types are electrochemical, biomimetic, and metal oxide, each using a different mechanism to detect the gas.

Electrochemical Detectors

The most common kind of detector, electrochemical, uses sensors made up of electrodes that are submerged in an electrolyte, a solution that conducts electricity. When CO enters the sensor, a chemical reaction causes electricity to flow through the electrolyte and the monitor alerts you, depending on how much the current increases.

These mechanisms last a long time, and they’re commonly used in high-quality models. You’ll still need to replace them based on the manufacturer’s recommendations though.

Biomimetic Detectors

Biomimetic detectors have a gel that mimics what happens when CO chemically attaches to the hemoglobin in the human body. CO can turn your blood a cherry red color because of its effect on blood proteins. The detector’s gel does the same thing when exposed to CO, and a light sensor inside watches for shifts in color and sounds the alarm when it becomes dangerous.

Metal Oxide Semiconductor Detectors

These lightweight and generally long-lasting detectors have metal oxide sensor chips inside them that change resistance when exposed to CO. The chips are coated with a porous metal oxide material that bonds easily with oxygen, making negatively charged ions.

When CO comes into the sensor, it has a stronger affinity than oxygen so the change in negative charge registers in the detector’s circuitry.

Fascinating detector science aside, there are plenty of options and each will need regular testing and replacement and require different installation.

Alarms

Detector alarms range from ear-piercing beeps to robotic voices telling you they sense dangerous levels of CO. Their alarms are loud in order to wake sleepers, because CO poisoning poses an extra threat to people who can’t feel the symptoms — such as headaches and dizziness — affecting them.

Installation

Some CO detectors use batteries and some are hard-wired. Some models plug directly into outlets, making them super simple to install right out of the box. Several models even offer a combination of fire and carbon monoxide monitoring. I have two of those in my house, and I appreciate the extra safety they provide. They’re hard-wired, so I don’t have to worry about batteries.

Most models need to be mounted to a wall or ceiling, just like smoke detectors.

Lifespan

Most CO detectors have a lifespan of five to seven years, but that can be shorter depending on the model. You’ll need to replace the whole alarm when it reaches the end of its life, and some will even let you know they’ve expired. A good rule of thumb is that if you can’t find an expiration date on your CO detector, replace it after seven years.

Check with an electronics recycling facility to see if they accept CO detectors. You may need to drop them off at a hazardous waste facility if your model has an internal backup battery.

Maintenance

Choose a day each quarter to test your CO detectors, but first make sure everyone in the vicinity knows it’s going to happen. Most models have a test button on their face or side. When you press the test button, be prepared for a loud, distinctive alarm. If you have a battery-powered model, consider swapping out the batteries at the same time.

Check the expiration date and take immediate action if it has passed. It’s something you don’t want to wait on.

Avoiding the Killer in the First Place

Taking preventive measures to keep CO out of your home goes a long way toward keeping you and your family safe. Below are a few tips to prevent it from happening in the first place. (The information goes well with our guide to home safety, in which we identify common household hazards and how to prevent them.)

Home Appliance Maintenance

Schedule or perform regular checks and maintenance on fuel-burning appliances — furnaces, water heaters, stoves, and fireplaces. Check for blockages and proper ventilation. Some hardware stores and Amazon also sell CO test kits, which can come in handy if you suspect a leaky appliance.

Check Your Ventilation

Proper airflow throughout a home can help prevent CO buildup. Check air vents, dryer vents, and ducts for obstructions, and consider having them cleaned if it’s been a while. That goes for chimneys and flues as well. They may need to be inspected and cleaned by professionals so blockages don’t happen.

If you live in snowstorm territory, make sure any low-lying dryer vents or other vents are clear of snow.

Avoid Portable Gas Appliances Indoors

Gas-powered generators, grills, and other portable fuel-burners need to stay outside and away from open windows and doors. That goes for attached garages as well.

Avoid warming a cold vehicle in a garage, even if the garage doors are open. Vehicles pump out a lot of CO when idling, and it can enter your home through drafts.

>>Read More: Testing Your Home, Inside and Out

Avoiding Disasters

CO should always be taken seriously. You can’t detect deadly concentrations of it without a detection device.

Equip your home with reliable detectors. Keep them working well and tested often, and replace them when needed. Following some of these lifesaving steps, as well as our guide to securing and protecting your home, will put you well on your way to avoiding potentially deadly disasters.

If you’re considering a comprehensive home security system, look for brands that bundle environmental sensors — CO, smoke, and water leak detection — into one integrated package for a stronger, more complete line of defense.