Testing · 7 min read
Continuous Radon Monitors
How continuous radon monitors work, what hourly data reveals, why tamper detection matters in transactions, and how to read a monitor report.
A continuous radon monitor is an electronic instrument that samples air repeatedly and reports a concentration for each hour, along with environmental conditions during the test.
The difference between a monitor report and a passive kit result is the difference between a video and a single photograph.
How they work
Air diffuses into a detection chamber where the instrument counts decay events, most commonly using a solid-state detector or a scintillation cell. Counts are converted to a concentration for each measurement interval.
Most professional monitors also record temperature, relative humidity, barometric pressure, and movement or tilt, and they timestamp every reading.
What hourly data reveals
Radon is not steady. Concentrations typically rise overnight when a house is closed and quiet, and fall during the day when doors open and wind increases air exchange.
Hourly data shows the shape of that cycle, which can be diagnostic. A flat, uniformly elevated profile suggests strong, steady soil gas entry. Sharp overnight peaks with low daytime values suggest ventilation is masking a real problem during the hours nobody is measuring.
Tamper detection and test integrity
In real estate testing, the credibility of the result depends on conditions being maintained. A monitor that logs a sudden humidity change, a temperature swing, and a motion event at 2 p.m. on day two tells the reader that something happened.
This is why continuous monitors are the professional standard in transactions. The report is auditable, and both parties can see the conditions rather than take them on faith.
Reading a monitor report
A well-prepared report includes several elements worth understanding.
- The test average, which is the headline number compared against 4.0 pCi/L.
- An hourly chart showing the pattern across the test period.
- Minimum and maximum hourly values, which show variability.
- Environmental data confirming closed-house compliance.
- Placement details: room, height, distance from walls and openings.
Consumer monitors
Inexpensive consumer monitors have become common and are genuinely useful for ongoing awareness in a home, particularly after mitigation, where they provide a running confirmation that levels stay low.
They generally lack the calibration documentation, tamper logging, and chain-of-custody suitable for a transaction, so they complement professional testing rather than replace it.
Key takeaways
- Continuous monitors report hourly concentrations plus test conditions.
- Hourly patterns distinguish steady entry from ventilation-masked problems.
- Tamper and environmental logging make results defensible in transactions.
- Consumer monitors are good for ongoing awareness, not for transactions.