Radon Detectors: Test Kits vs. Continuous Monitors
A radon detector reports how much radioactive radon gas is in your indoor air, measured in picocuries per liter (pCi/L). But “radon detector” covers four very different products at wildly different prices: a $20 lab kit you mail in, a $200 plug-in monitor that talks to your phone, and a $2,000 professional instrument rented by the day for real-estate deals. They are not interchangeable. This guide sorts out which one actually answers your question, whether that question is “is my house safe to live in” or “does this house I’m buying pass the radon contingency.”
Two ways detectors actually measure radon
Every radon device belongs to one of two families. Passive detectors collect radon over a fixed window and are read later. Alpha-track kits use a plastic film that records microscopic damage from alpha particles emitted as radon decays; a lab counts the tracks under a microscope. Charcoal canisters adsorb radon during a short deployment, then a lab measures the trapped radioactivity by gamma spectroscopy. Electret ion chambers read the drop in charge on a statically charged disc. All three give you one number for the whole test period and nothing in between.
Active detectors — continuous radon monitors, or CRMs — count decay events electronically in real time using an ionization chamber or a silicon photodiode, and display an updated pCi/L value on the device or in an app. That difference in mechanism is the difference in what you can learn: a passive kit tells you an average; a CRM tells you the story behind the average.
The four detector tiers, and what each one is for
| Detector | Typical cost | Result timing | Best for |
|---|---|---|---|
| Short-term kit (charcoal / alpha-track) | $15–$30 incl. lab fee | 2–7 day test, results 1–3 weeks | First-time screening |
| Long-term kit (alpha-track / electret) | $30–$100 incl. lab fee | 90 days to 1 year | Definitive annual average; post-mitigation confirmation |
| Consumer CRM (AirThings, RadonEye) | $150–$400 | First reading in 24 hr, refines over weeks | Ongoing household monitoring |
| Professional CRM (rented) | $100–$300 rental | 48 hr–7 day documented test | Real-estate transactions |
Short-term kits are the cheapest way to find out if you have a problem at all, and many Colorado county health departments hand them out free or subsidized through the state program. Their weakness is that a single winter week can run high and a single summer week can run low, so the EPA treats a short-term result as a screen, not a verdict. Long-term kits fix that by integrating a full season or more, which is why they produce the most defensible annual average — at the cost of waiting three months for an answer that no home sale will wait for. The radon gas test kit guide compares the mail-in options in detail.
What consumer continuous monitors add
Consumer CRMs are the fastest-growing tier because they answer a question kits can’t: why your radon moves. The AirThings Wave Plus and View Radon and the Ecosense RadonEye RD200 all sit in the $150–$400 range, show a live pCi/L reading and a rolling long-term average, and log the data to a phone app. Watch one for a month and you’ll see radon climb on a cold, still night, drop when the furnace fan runs, and spike during a wind storm — patterns a one-week kit erases into a single number.
The trade-off is accuracy. Consumer units generally claim roughly ±10–20% at residential concentrations, which is fine for deciding whether to mitigate but short of transaction-grade documentation. RadonEye tends to focus purely on radon with fast response; AirThings bundles CO₂, humidity, VOC and temperature sensors and deeper smart-home integration. For a household that wants to keep an eye on levels year-round and verify a mitigation system indefinitely, a consumer CRM has the best information-per-dollar of any tier.
Why a professional monitor is different — and required for sales
You cannot substitute a $250 consumer monitor for a real-estate radon test, and it isn’t about accuracy alone. Professional CRMs (Sun Nuclear, Radalink, Femto-Tech) add tamper detection that flags if the unit was moved or covered, motion and humidity logging that documents the test conditions, and chain-of-custody data the result can stand on if a buyer disputes it. AARST/NRPP measurement protocols call for exactly these features on a transaction test. That’s why the sensible pattern is to own a consumer CRM for your own peace of mind and rent a professional one — or hire a certified measurement pro — only when a closing depends on it. Budget for both together in overall radon testing costs.
Reading the number: pCi/L, Bq/m³, and the 4.0 line
U.S. detectors read in pCi/L; European ones read in becquerels per cubic meter, and 1 pCi/L equals 37 Bq/m³. The EPA action level is 4 pCi/L (148 Bq/m³) — at or above that long-term average, the EPA recommends you mitigate — and it suggests considering action between 2 and 4 pCi/L, since no radon level is risk-free. The World Health Organization sets its reference lower, at 100 Bq/m³ (about 2.7 pCi/L). Radon is the second-leading cause of lung cancer after smoking and the leading cause among people who never smoked.
The trap with a live CRM display is fixating on the peak. A real Front Range basement might read 1 pCi/L on a calm summer afternoon and 8 pCi/L on a windy January night. The number that drives a mitigation decision is the rolling long-term average, not the worst single spike. Use the average; ignore the drama. For the full risk framing see what counts as a safe radon level.
Placement makes or breaks the reading
Put the detector on the lowest lived-in level — a finished basement, or the lowest occupied floor. EPA placement rules call for a spot 20 to 72 inches off the floor (about bookshelf height), at least 4 inches from interior walls and 12 inches from exterior walls, away from drafts (windows, exterior doors, supply registers, fans) and away from kitchens, baths, and laundry rooms where humidity swings distort readings. Keep it roughly central rather than jammed into a foundation corner, where radon pools and reads artificially high.
Test conditions matter as much as location. Short-term tests require closed-house conditions: windows and exterior doors shut except for normal comings and goings, no window or whole-house fans, HVAC running normally. Skip testing during high winds or heavy storms, which shift the indoor-outdoor pressure that drives soil gas in. More detail lives in the radon test placement guide.
Colorado Front Range context
Most of the Front Range sits in EPA Radon Zone 1, the highest-potential tier, so an elevated reading here is common rather than freakish — CDPHE reports roughly half of tested Colorado homes come back at or above 4 pCi/L. That’s an argument for owning a monitor rather than testing once and forgetting it. If your long-term average holds at or above 4 pCi/L, a NRPP- or NRSB-certified contractor can install sub-slab depressurization, usually in a day, cutting indoor levels by 80–99% for a typical $1,200–$2,500 Colorado job. Leave the CRM running afterward: a creeping average is the earliest sign a mitigation fan has failed. See how radon mitigation works, or browse the full radon testing hub.
Frequently asked questions
What’s the best radon detector for a home I already own? A consumer continuous monitor (AirThings Wave Plus or RadonEye RD200, $150–$400) for year-round visibility, or a long-term alpha-track kit ($30–$100) if you just want one solid annual average and no app. Short-term kits are the cheapest way to find out whether you need to look harder.
Can I use my consumer monitor for a home sale? No. Transactions call for a certified professional using a tamper-detecting CRM with chain-of-custody logging. Keep your consumer unit for personal monitoring and hire out the transaction test.
Do these detectors need calibration? Consumer CRMs are factory-calibrated and generally need nothing beyond fresh batteries and clean air around the sensor. Professional units are recalibrated annually at an accredited facility — a cost the pro absorbs, not the renter.
Does a radon detector measure radon in well water? No — air detectors measure airborne radon only. If you’re on a private well in a high-radon area, water radon needs a separate lab sample; Front Range homes on municipal water don’t.
Front Range homeowners choosing a monitor or needing a certified pro for a transaction test can contact us for a vetted referral. This guide reflects EPA and CDPHE guidance current as of 2026; confirm site-specific decisions with a certified radon professional.
References
- EPA — Health Risk of Radon (4 pCi/L action level)
- EPA — A Citizen’s Guide to Radon
- CDC — About Radon
- CDPHE — Colorado Radon Program
- American Lung Association — Radon
Continuous radon detectors
A digital monitor gives you an always-on reading and a long-term average — better than a one-shot kit if you want to track levels over time.
| Product | Why | Buy |
|---|---|---|
 Airthings Corentium Home | Battery, portable; trusted long-term average. | Amazon — $149.99 |
 Ecosense RadonEye RD200 | Fast first reading (~1 hr); app logging. | Amazon — $160.54 |
 Airthings View Plus | Radon + CO2 + PM + VOC in one unit. | Amazon — $279.99 |