QORVAN

How Radon Sensors Work

Charcoal canisters, electret ion chambers, alpha track detectors and continuous monitors measure radon in different ways. Here's how each works.

Updated · 2 min read · By QORVAN Editorial Team · Reviewed by QORVAN Product Team

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Every radon detector works by counting the radiation that radon and its progeny emit — but they differ in when they count, how much air they sample and how the result reaches you.

Passive detectors

MethodHow it worksTypical use
Charcoal canisterCharcoal adsorbs radon over 2–7 days; the canister is sealed and analysed in a labQuick short-term screening
Alpha trackAlpha particles from the decay of collected progeny leave microscopic tracks in a plastic sheet, counted laterLong-term measurement (months)
Electret ion chamberRadon decays inside a chamber and discharges an electret; the voltage change gives the averageShort- and long-term tests

Passive detectors are simple and need no power. In exchange, you get one average, after the fact, with no visibility into what happened during the exposure.

Continuous monitors

A continuous monitor draws air into a small chamber and counts the alpha decays of radon and progeny with a solid-state detector, reporting a concentration every few minutes to a few hours. Because it runs continuously, it can show:

  • how levels change overnight and with weather,
  • the difference between a short-time reading and a long-time average,
  • whether a mitigation system is working.

The trade-off is that it needs power, and its readings depend on the sensor’s calibration and update interval.

Matching the method to the question

  • “Is my home above the action level?” — a compliant test with an accepted method and protocol.
  • “Is it changing, and which room is worse?” — a continuous monitor.
  • “What is my year-round average?” — a long-term test (or months of continuous data).

Whatever the method, placement drives whether the number means anything. Read where to put a radon detector.

Frequently asked questions

Which type of radon detector is most accurate?
Accuracy depends on method, calibration and measurement time. For a compliance test, use a device and protocol accepted by your local authority. For understanding trends, a continuous monitor is more useful.
Why does a charcoal test tell me nothing for days?
Charcoal canisters adsorb radon over the exposure period and are then sealed and sent to a lab, so the result arrives after the test ends.

Sources

  1. A Citizen's Guide to Radon — U.S. EPA
  2. Radon and health (fact sheet) — World Health Organization