Carbon monoxide is a deadly gas produced when fossil fuels are burned. It is colorless, odorless and silent, making it almost impossible to detect on its own until it is too late. CO poisoning is completely preventable with proper use of carbon monoxide detectors.

Carbon monoxide blocks your blood’s ability to carry oxygen. Specifically, it replaces the place where oxygen normally takes up hemoglobin in red blood cells by binding it more tightly. When your blood can no longer do its job of carrying the oxygen your body needs to keep your organs going, especially your brain, your organs shut down.

The risk of CO poisoning is particularly severe at winter or when the power goes out when gasoline-powered appliances such as furnaces or portable generators are likely to operate.

Fortunately, it’s not all doom and gloom. If you change your carbon monoxide detector batteries twice a year, and set them to wake you up when you sleep, they will protect you from CO poisoning. You may want to consider a CO detector with a digital readout as that will tell you the maximum CO level in your home in addition to sounding the alarm. (You can check out our guide on the best place to put your smoke detector.)

What are the most common causes of CO in people’s homes?

You may be wondering what causes carbon monoxide in and around a home, and there are many common causes. Anything that burns fossil fuels is a potential hazard. This list includes (but is not limited to) cars, trucks, ovensstove, gas rangessmall machines, generators, grillslanterns and fireplaces. Improper use or maintenance of these devices can cause CO to build up to lethal levels in your home.

What are the signs of a CO leak?

Carbon monoxide is odorless; it is odorless. Without a CO detector, you may not notice a CO leak until it’s too late. That’s why it’s important to have CO detectors in your home that can detect low levels of carbon monoxide before they become dangerous.

How dangerous is CO?

Carbon monoxide is deadly. Symptoms of carbon monoxide poisoning are often described as flu-like, including headache, nausea, vomiting, chest pain, dizziness, weakness and confusion. A sleeping person would likely not register these symptoms and could easily die in their sleep. Also, CO itself can make you sleepy and then kill you. Everyone is at risk of CO poisoning, but infants and the elderly are particularly susceptible, as are people with heart problems, anemia and breathing issues. According to the CDCmore than 400 people in the US die from unintentional CO poisoning unrelated to fire, more than 100,000 emergency room visits and more than 14,000 hospitalizations each year.

How do CO detectors work?

CO detectors measure the concentration of carbon monoxide in the air, triggering an alarm if it is high enough. There are several different types of CO sensors, including biometric gel, metal oxide semiconductor, and electrochemical. For more details on how accurate CO detectors are, see our explainer.

Whatever type of CO detector you have, be sure to place it where you can hear the alarm while you sleep. A good CO detector, in addition to detecting sudden spikes, can detect even low levels of CO over time. This could indicate a slow gas leak somewhere in your home.

Where do you put the CO detector?

Every floor of your home, including the basement, should have a CO detector, according to the EPA. Be sure to place a CO detector within 10 feet of every separate bedroom in your home, so that it will wake anyone who may be asleep when it sounds. There must also be one within 20 feet of any attached garage, furnace, water heater and fireplace. Wherever you place your carbon monoxide detector, make sure the areas are free of obstructions and protected from adverse environmental conditions.

Check out our guide for more CO detector installation tips. Be sure to read and follow the CO detector manufacturer’s instructions for installing and maintaining the device.

What do I do if my CO detector goes off?

If a carbon monoxide alarm sounds, get everyone out of the house and get fresh air immediately and then call emergency services. It takes time for carbon monoxide to dissipate, so don’t assume it’s safe to return to your home when the alarm goes off. Always make sure your CO detector has fresh batteries; changing it twice a year at the same time we change our clocks Daylight Saving Time a great way to help you remember.

Is there another way to detect CO?

You can’t detect carbon monoxide no CO detector, but you can identify potential CO hazards around your home.

Poorly maintained and poorly ventilated gas-fueled household appliances are the most common causes, so be sure to keep an eye on them. These potential hazards include brownish or yellowing stains around appliances, pilot lights that go out frequently, yellow (instead of clear blue) burner flames, no upward draft in your chimney flue, smelly air, and soot or smoke in your house.

What are the best ways to prevent CO leaks?

Make sure your chimney is in place, heating system, water heater and any other appliances that burn gas, oil or coal serviced annually by a qualified technician. If you see, smell or feel anything “off,” get it checked out right away.

Only buy gas equipment if it has the seal of the national testing agency such as Underwriters’ Laboratories. Make sure your gas appliances are properly vented; The horizontal vent pipes should rise slightly as they go outward.

Never try to patch a vent pipe with tape or gum or anything else. Do not use a gas oven to heat your home. Do not burn charcoal inside your home.

Do not use portable gas camp stoves or portable flameless chemical heaters indoors. If you use a generatordon’t use it inside your house or garage — or even within 20 feet of any window or vent. All of these things can cause carbon monoxide to build up in your home. For backup power, consider options such as a solar generator or portable power stationthat does not burn fossil fuels or pose a carbon monoxide hazard.

You should avoid driving a car inside a closed garage. Did you know that you should not run your car in an attached garage even if the garage door is open? I used to do it on cold winter days to warm up my car, but I definitely won’t do it again. It’s also a good idea to have a mechanic check-up your car’s exhaust every year. If you drive a vehicle with a tailgate, be sure to open the vents or windows when the tailgate is open.

For more home safety tips, check out our home security cheat sheetand how to protect against fire, mold and other household hazards.