You cannot see, smell, or taste radon, so the only way to know if it’s in your home is to test for it. Radon is a naturally occurring radioactive gas that seeps up from the soil and can accumulate indoors, and it’s responsible for an estimated 21,000 lung cancer deaths in the United States every year. No physical symptom or sensory clue will tip you off. Testing is simple, inexpensive, and something you can do yourself in a weekend.
Why You Can’t Detect Radon Without a Test
Radon is colorless, odorless, and tasteless. It forms naturally as uranium in soil and rock breaks down, and it enters homes through cracks in foundations, gaps around pipes, and other openings where the building contacts the ground. Once inside, it can build up to concentrations that pose a serious health risk, all without any visible sign. There’s no stain on your walls, no unusual smell, and no way your body can sense it. The National Institute of Environmental Health Sciences calls it “an invisible enemy” for exactly this reason.
Any home can have elevated radon, regardless of age, construction type, or geographic region. New homes are not safer than old ones. Homes without basements are not immune. Two houses on the same street can have dramatically different levels. The only variable that matters is what’s happening in the soil beneath your specific foundation, which is why individual testing is essential.
Short-Term Test Kits
The fastest and cheapest way to check your home is a short-term test kit, typically a small canister of activated charcoal that you leave in place for two to seven days. These kits cost roughly $10 to $30 at hardware stores or online, and some state radon programs offer them free or at a discount. You expose the canister, seal it back up, and mail it to a lab. Results usually come back within a week or two.
Short-term kits are useful as an initial screening tool, but they have a significant limitation: they capture a snapshot, not a full picture. Radon levels inside a home fluctuate with weather, wind, heating patterns, and how tightly the house is sealed. A study of over 1,000 homes at the University of Massachusetts found that when estimating a home’s true annual radon concentration from a single charcoal test, the uncertainty was roughly plus or minus 90 percent at a high confidence level. That means a reading of 4 could reflect an actual annual average anywhere from below 1 to nearly 8. A short-term test that comes back high is a reliable signal to investigate further. A short-term test that comes back low doesn’t guarantee you’re safe year-round.
Long-Term Test Kits
For a more accurate reading, long-term alpha-track detectors measure radon over 90 days or more. These small devices contain a piece of plastic film that records tiny marks each time a radon particle strikes it. Because they sample over months rather than days, they smooth out the daily and weekly fluctuations that make short-term tests unreliable. The same University of Massachusetts study found that alpha-track detectors had an uncertainty of roughly plus or minus 50 percent at the 90 percent confidence level, and plus or minus 25 percent at a standard confidence level. That’s a much tighter estimate of what you’re actually breathing over time.
Alpha-track detectors also handle humidity and temperature swings better than charcoal canisters, which can lose accuracy in damp conditions. If you plan to live in your home for years, a long-term test gives you the most trustworthy number to base decisions on.
Continuous Digital Monitors
Plug-in electronic radon monitors offer ongoing, real-time readings. Devices like the Ecosense EcoQube or Safety Siren Pro4 sit in your home permanently and display both short-term and long-term average concentrations, sometimes with trend charts and smartphone access. Prices typically range from about $130 to $200. These monitors let you see how radon levels shift with the seasons, which is valuable information if you’re near the action threshold and trying to decide whether mitigation is worth it.
Professional Radon Testing
A certified radon professional typically charges $150 to $250 for an in-home test. Professionals use continuous monitoring devices that require electrical power and record radon levels throughout the entire test period, producing a detailed hourly or daily log. This is the standard approach during real estate transactions because it’s harder to tamper with and generates a documented chain of custody. If you’re buying or selling a home, most states require that any existing radon test results be disclosed on the property disclosure form.
Where and When to Place a Test
The CDC recommends placing your test device in the basement or the lowest level of your home that you actually use as living space. The device should be raised about three feet off the ground and positioned in the middle of the room, away from exterior walls, windows, and vents. Drafts and direct sunlight can distort readings. Keep windows and exterior doors closed as much as possible during the test period, aside from normal entry and exit.
Winter is the best season to test. When your home is buttoned up against the cold with doors and windows sealed, radon has the least opportunity to escape and the most opportunity to accumulate. The EPA specifically recommends testing during the colder months for the most accurate reading. That said, testing in any season is better than not testing at all.
Understanding Your Results
Radon is measured in picocuries per liter (pCi/L). The EPA sets its action level at 4 pCi/L: if your home tests at or above that number, the recommendation is to fix the problem. The agency also encourages homeowners to consider mitigation for levels between 2 and 4 pCi/L. There is no known safe level of radon exposure. Risk increases proportionally with concentration and the number of years you’re exposed.
If a short-term test comes back at or above 4 pCi/L, the standard next step is to run a second short-term test or a long-term test to confirm the result before investing in a mitigation system. If a short-term test comes back below 2 pCi/L, your risk is relatively low, though retesting every few years is still a good idea since soil conditions and home settling can change over time.
What Happens if Levels Are High
The most common and reliable fix is called active sub-slab suction. A contractor installs a pipe through the foundation slab into the gravel or soil beneath your home, then attaches a fan that continuously pulls radon-laden air from under the house and vents it above the roofline, where it disperses harmlessly. This method reduces indoor radon by 50 to 99 percent, depending on the home’s construction and soil characteristics. Some systems achieve reductions near 99 percent.
Installation typically takes a day. The system runs continuously and uses about as much electricity as a light bulb. After installation, you retest to confirm that levels have dropped below 4 pCi/L, ideally below 2. The pipe and fan are unobtrusive, and the ongoing cost is minimal. For a problem that contributes to 21,000 lung cancer deaths annually in the U.S., it’s one of the more straightforward home safety fixes available.