Radon Detectors: What Homeowners Need to Know
Radon detectors fall into four practical categories, each suited to a different homeowner use case. Charcoal canisters give a 2- to 7-day average for fast decisions. Alpha-track detectors give a 3- to 12-month average for annual baselines. Electret ion chambers are the professional semi-passive option. Continuous radon monitors (CRMs) deliver hourly readings and a long-running average — the consumer-grade versions from Airthings, Ecosense (RadonEye), and Corentium have become standard tools in Front Range homes where Colorado’s Radon Zone 1 geology makes ongoing tracking a sensible habit. This guide walks through what each detector measures, where to place it, what to expect for pricing, and how to read a reading against EPA, WHO, and CDPHE thresholds. This article summarizes EPA, WHO, CDPHE, and CDC guidance current as of 2026; see our methodology page for sourcing — and remember the linear no-threshold model: no level of indoor radon is truly safe, only lower-risk.
What are the main types of radon detectors?
Charcoal canisters (passive, short-term)
Activated charcoal absorbs radon from the air during a 2- to 7-day deployment. The homeowner seals the canister and mails it to a certified lab, which measures radon by gamma spectroscopy of the radon daughters absorbed in the charcoal. Pricing: $10 to $30 per kit including lab analysis. Strengths: cheapest entry point, EPA-recognized, used by NRPP-listed pros for real-estate short-term tests. Limitations: single-point reading, no per-hour data, requires closed-house conditions during deployment.
Alpha-track detectors (passive, long-term)
A small plastic film registers etched tracks as alpha particles from radon decay strike it. After 90 days to a year of deployment, the homeowner mails the detector to the lab, which counts tracks under a microscope to derive a time-weighted average. Pricing: $20 to $50 per kit including lab analysis. Strengths: annual exposure baseline, smooths seasonal variation, EPA-recognized for long-term measurement. Limitations: long wait for results, single number per deployment.
Electret ion chambers (semi-passive, professional)
An electrostatically charged disc inside a chamber loses charge proportionally to alpha particle exposure. Used by professionals because the disc requires reader equipment to interpret. Not a consumer device.
Continuous radon monitors (active, real-time)
Electronic devices that sample radon hourly using ionization chambers or alpha-track silicon photodiodes. Consumer-grade brands (Airthings View Radon, Airthings View Plus, Ecosense RadonEye, Corentium Home) display rolling 24-hour, 7-day, and long-term averages. Pricing: $150 to $300 consumer-grade, $800 to $2,500 NRPP-listed professional. Strengths: continuous data, no per-test fees, mitigation verification, seasonal visibility. Limitations: higher upfront cost, consumer models not NRPP-listed for real estate transactions, calibration drift over multi-year operation.
Choosing the right radon detector for the use case
Real estate transaction
A NRPP-listed measurement professional running a 48-hour continuous radon monitor under closed-house conditions. The CRM produces per-hour data that flags tampering and supplies a defensible reading for the inspection-objection negotiation. Cost: typically $150 to $250 as part of the inspection bundle in metro Denver. See our radon testing cost breakdown for the Front Range bundled pricing.
Annual baseline for a current homeowner
An alpha-track detector deployed for 90 days to a year in the lowest occupied level. The annual average is the right number for cancer-risk extrapolation. Cheaper than a CRM if a one-time baseline is the goal.
Post-mitigation verification
A short-term charcoal canister test, a NRPP-listed CRM test, or a consumer-grade CRM left running for 30 to 90 days after the system is operating. The mitigator usually provides a short-term post-mitigation test; the homeowner’s own CRM gives ongoing confirmation that the fan continues to perform.
Ongoing daily tracking
A consumer-grade CRM left in the lowest occupied level. The device is most useful in homes with mitigation systems (verifies fan performance), homes near the EPA action level (catches seasonal spikes), and homes where occupants want to understand how radon varies with weather and home use.
Where to place a radon detector
EPA placement guidance is consistent across detector types:
- Lowest occupied level — basement living area or finished basement bedroom on the Front Range; first floor if no occupied basement
- Breathing height — 2 to 6 feet above the floor (table or shelf height)
- At least 3 feet from exterior walls, windows, doors, and HVAC vents
- At least 12 inches from the ceiling
- Away from drafts, humidity, and direct sunlight
- Not on a fireplace mantel (heat affects some detector chemistries)
Closed-house conditions apply to short-term tests (less than 4 days): windows and exterior doors closed except for normal entry and exit, HVAC operates normally, no whole-house fans or continuous exhaust. The closed-house window starts 12 hours before the test and continues through the deployment.
Reading a radon detector result
Reference numbers:
- EPA action level — 4 pCi/L (mitigation recommended)
- EPA “consider action” range — 2 to 4 pCi/L
- WHO reference level — 2.7 pCi/L (100 Bq/m³)
- U.S. indoor average — about 1.3 pCi/L
- Colorado indoor average — 2 to 4 pCi/L per CDPHE
- Outdoor average — about 0.4 pCi/L
About half of tested Colorado homes read at or above the EPA action level of 4 pCi/L because the state sits in EPA Radon Zone 1, the highest predicted-radon-potential band. A 6 pCi/L reading on the Front Range is common — and it is also above the EPA action level and warrants mitigation. The Front Range radon testing pillar walks through Colorado-specific context.
Consumer CRM brands in 2026
Airthings View Radon and View Plus
Wi-Fi enabled, app-connected, $200 to $300. The View Plus adds CO₂, VOC, humidity, temperature, and barometric pressure sensors alongside the radon ionization chamber. Long-term residential monitoring is the design intent.
Ecosense RadonEye
$150 to $200. Uses an ionization chamber and reports on an onboard screen plus a smartphone app. Faster equilibration than passive detectors — useful results within 1 hour, stable readings within 24.
Corentium Home
$170 to $220. Battery-powered, no Wi-Fi required, displays 1-day, 7-day, and long-term averages on the device screen. Simple and accurate.
Independent testing (e.g., by certified labs and university radiation programs) shows these consumer brands track well against NRPP-listed professional CRMs over time. None of them are NRPP-listed for real estate use, but all are appropriate for ongoing homeowner monitoring.
Calibration and drift
Consumer CRMs drift over time as the sensor ages. Most manufacturers recommend recalibration every 2 years for accuracy beyond ±10%. Some manufacturers offer a calibration service; others recommend cross-comparing against a short-term passive kit annually to confirm the device is reading within tolerance. Passive detectors (charcoal canisters and alpha-track) are fresh-from-factory each test and do not have a calibration drift concern.
Front Range seasonal variation
Indoor radon in Colorado homes varies seasonally:
- Winter — typically highest. Tight, heated homes pull more soil gas through the foundation; closed windows trap radon.
- Summer — typically lower. Open windows and reduced heating-driven pressure differentials let radon escape.
- Spring and fall — variable, often in between.
This is one reason long-term alpha-track or continuous-monitor data is more useful than a single short-term reading for understanding annual exposure. A 6 pCi/L February reading and a 3 pCi/L July reading describe the same home — the annual average is the right number for risk extrapolation.
How radon detectors fit into a Front Range homeowner’s routine
The practical pattern for many Colorado homeowners is to combine a one-time professional measurement with ongoing consumer-grade monitoring:
- Pre-purchase — NRPP-listed professional 48-hour CRM test as part of the home inspection, under closed-house conditions
- Post-mitigation — NRPP-listed professional short-term test 30 to 90 days after the mitigation system is installed
- Ongoing — consumer-grade CRM (Airthings, RadonEye, Corentium Home) left running in the lowest occupied level for daily tracking
- Every 2 years — short-term passive test (charcoal canister or alpha-track) for cross-comparison against the CRM, plus a fresh annual baseline
- After major renovation — short-term test to confirm soil-gas entry has not changed
This layered approach combines the defensibility of professional measurement at the moments when documentation matters (real estate, post-mitigation) with the continuous visibility of consumer-grade monitoring during normal homeownership. It catches sensor drift, fan failures in mitigation systems, and seasonal spikes that a single annual reading would miss.
Common mistakes when using radon detectors
Three patterns reduce the usefulness of home radon detection:
Placing the detector in the wrong location
Detectors placed in unfinished utility rooms, near sump pumps, or close to the HVAC return air register can produce misleadingly high or low readings. EPA placement guidance — lowest occupied level, breathing height, away from drafts and HVAC registers — exists for a reason.
Reacting to single-hour readings on a CRM
Consumer CRMs display hourly readings that can spike or dip based on weather, HVAC operation, or window openings. The rolling 24-hour, 7-day, and long-term averages are the actionable numbers. Single-hour spikes are normal and do not require action.
Forgetting to recalibrate or cross-check
Consumer CRMs drift over multi-year operation. Most manufacturers recommend cross-comparison against a fresh short-term passive kit every 1 to 2 years. The cross-check costs $10 to $30 and confirms the CRM is reading within tolerance.
When to call a professional
Call a NRPP-listed measurement professional for any real estate transaction. Call a NRPP-listed mitigation contractor when readings land at or above the EPA action level. Call your physician about lung-cancer risk if you are a current or former smoker living with elevated indoor radon. Use consumer-grade detectors for ongoing visibility, not for real-estate-binding readings.
References
- EPA Citizen’s Guide to Radon — U.S. Environmental Protection Agency
- EPA Map of Radon Zones — U.S. Environmental Protection Agency
- CDPHE Colorado radon program — Colorado Department of Public Health and Environment
- CDC radon and health — Centers for Disease Control and Prevention
Front Range homeowners who want a connection to a NRPP-listed radon professional for testing or mitigation can reach out through our contact page. Colorado geology makes radon a near-universal concern in Zone 1, and a confirmed reading from a vetted professional is the foundation for any mitigation or post-mitigation decision.