The short answer
Radon and carbon monoxide are both colorless and odorless, which is the only reason people confuse them. Radon is a naturally radioactive gas that rises out of the soil and raises your lung cancer risk over years, with no immediate symptoms. Carbon monoxide is a gas made by burning fuel, and it can poison you within minutes at high levels. They are different hazards detected by different devices. A carbon monoxide detector does not detect radon, and a radon test does not detect carbon monoxide. To be protected, you need a CO alarm and a separate radon test.
1. What radon is
Radon is a naturally occurring radioactive gas. It forms underground as uranium in soil and rock breaks down over time, and it has no color, no smell, and no taste. Because it is a gas, it moves up through the ground and seeps into buildings through cracks in the foundation, gaps around pipes, sump pits, crawl spaces, and other openings where the house meets the soil.
The key thing to understand is the source. Radon is not produced by anything inside your home. It comes from the earth underneath and around it, so every home sits on a different amount of it depending on the local geology. That is also why radon levels tend to be highest in the lowest level of a house, such as a basement or a slab-on-grade floor, where the air is in closest contact with the soil. For a deeper look at the entry pathways, see our guide on how radon enters your home.
2. What carbon monoxide is
Carbon monoxide, often written as CO, is produced when fuel does not burn completely. Like radon, it is colorless and odorless, which is where the similarity ends. The source is not the ground. It is combustion happening inside or near your home: a furnace or water heater that is not venting properly, a gas range, a wood stove or fireplace, a portable generator, a charcoal grill used indoors, or a car left running in an attached garage.
Because CO comes from appliances and engines rather than the soil, the risk goes up when something is broken, blocked, or used the wrong way. A cracked heat exchanger, a clogged flue, or a generator run too close to the house can push CO indoors fast. That fundamental difference, an outside-the-home soil source versus an inside-the-home combustion source, is why the two gases behave so differently and need to be handled in completely different ways.
3. Side by side: how they differ
It helps to put the two next to each other. They share only the two traits that make them sneaky, being invisible and odorless. On every other count that matters, they are opposites.
| Radon | Carbon monoxide | |
|---|---|---|
| Source | Soil and rock under the home | Incomplete fuel combustion |
| Type of hazard | Radioactive, cancer risk | Toxic, acute poisoning |
| Timeline of harm | Years of exposure | Minutes to hours |
| Symptoms | None until lung cancer develops | Headache, dizziness, nausea, collapse |
| Colorless and odorless | Yes | Yes |
| How you find it | Radon test (kit or monitor) | CO alarm |
| The fix | Radon mitigation system | Repair or vent the appliance |
4. Health effects of radon
Radon hurts you slowly and silently. When you breathe it in, radioactive particles can lodge in the lining of your lungs and, over years, damage the cells there. That accumulated damage is what raises cancer risk. Radon is the second leading cause of lung cancer in the United States after smoking, and it is the leading cause among people who have never smoked.
The part that catches people off guard is that there are no warning signs. Radon exposure does not make you cough, give you a headache, or set off any sensation at all. You can live in a home with a high radon level for years and feel completely normal the entire time, while the risk quietly builds. That is exactly why testing matters so much: the gas gives you no other clue. We cover the topic in more depth in our article on radon exposure symptoms.
5. Health effects of carbon monoxide
Carbon monoxide does the opposite. It harms you fast. When you breathe CO, it binds to your blood far more readily than oxygen does, which starves your organs of the oxygen they need. At high concentrations this can happen within minutes, and it can be fatal.
Unlike radon, carbon monoxide poisoning does produce symptoms, though they are easy to mistake for the flu: headache, dizziness, weakness, nausea, confusion, and, at higher exposures, loss of consciousness. A telltale clue is when several people in the same home feel sick at once and feel better after leaving the building. Because CO acts so quickly, this is the hazard where you act immediately.
If a CO alarm sounds or anyone has symptoms of carbon monoxide poisoning, get everyone outside to fresh air right away and call 911 or your gas utility. Do not wait. This is an emergency, and it is very different from a high radon reading, which is serious but never an immediate, get-out-now situation.
6. Why a CO alarm cannot detect radon
This is the single most important point in the whole article, so it is worth stating plainly. A carbon monoxide detector does not detect radon. A radon test does not detect carbon monoxide. They measure two completely different things using two completely different methods.
A CO alarm has a sensor tuned to the carbon monoxide molecule. When CO in the air rises past a set threshold, the sensor reacts and the alarm sounds. It has no ability to sense radioactivity, so it is blind to radon no matter how high the radon level climbs. A radon measurement works the other way around. It detects the radioactive decay of radon over a set period, either with a passive test kit you send to a lab or a continuous radon monitor that logs levels electronically. That device has no way to sense carbon monoxide.
Having working CO alarms in your home tells you nothing about your radon level. A house can have a CO alarm on every floor and still have a dangerous radon problem that no alarm will ever flag. The only way to know your radon level is to run a radon test.
A handful of combination units on the market do combine a CO alarm with a radon monitor in one housing, but that is two separate sensors packaged together, not one sensor doing both jobs. The takeaway is the same: do not assume one device is covering the other hazard.
7. What to do about each one
Because they are different hazards, they call for different actions, and you want both covered.
For carbon monoxide
Install CO alarms on every level of your home and near sleeping areas, test them regularly, and replace them on the manufacturer's schedule. Have fuel-burning appliances such as your furnace, water heater, and fireplace inspected and serviced by a qualified HVAC professional, keep flues and vents clear, and never run a generator, grill, or vehicle in an enclosed space. CO problems are usually solved by repairing or properly venting the appliance that is producing the gas.
For radon
Test your home for radon. A test is the only way to find it, and it is inexpensive and straightforward. If the result comes back at or above the EPA action level of 4.0 pCi/L, the fix is a radon mitigation system, most often a sub-slab depressurization setup that pulls soil gas from beneath the foundation and vents it safely above the roofline. After mitigation, a follow-up test confirms the level has dropped. For more on why this step is not optional, read why radon testing is essential, or learn about our radon testing service.
When you hire a radon professional, it is reasonable to look for credentials from a recognized program such as NRPP or NRSB. Those are good signals of training for any company you consider.
8. Why this matters in metro Atlanta
The radon side of this comparison is especially relevant here. Much of metro Atlanta sits on granite and uranium-bearing bedrock, and several area counties, including Fulton, Cobb, DeKalb, and Gwinnett, fall in the EPA's highest radon zone. That means a predicted average at or above the action level, and elevated home results are common across the region.
Georgia does not have a state radon testing law, so the responsibility sits with the homeowner. Plenty of local homeowners have CO alarms installed and assume they are covered, then are surprised to learn those alarms say nothing about radon. If you have never tested your home for radon, that is the gap worth closing, because in this part of the country the odds of an elevated reading are real.
9. Frequently asked questions
This article is general information for homeowners, not medical, safety, or engineering advice. If you suspect a carbon monoxide problem, treat it as an emergency, get to fresh air, and call 911 or your gas utility. For radon, the right next step is a test followed by mitigation if levels are elevated. Confirm specifics that apply to your home with a qualified professional.
