Aranet Radon Plus

Aranet's datasheet describes the detector as alpha decay event detection with an ionization chamber, filled by air diffusion. There is no pump: air drifts into a 137 cm³ chamber through a spunbound polyester filter that keeps out radon's decay products, so the sensor counts the alpha particles from radon that has entered and decayed inside. Aranet rates its efficiency at 1 count per minute at 2.3 pCi/L.

The datasheet also says plainly what the sensor cannot do: it has no radon and thoron discrimination, so it cannot tell radon from thoron, a related gas. The same table gives the chamber's volume, its filter material and its counting efficiency, the figures above.

The reading updates every 10 minutes. The first number appears about 10 minutes after the batteries go in, and Aranet says full measurement accuracy takes 1 hour. A switch on the side moves the screen between the 10-minute reading and 24-hour, 7-day and 30-day averages; if the device has not run as long as the chosen average, a status mark says so. The published range is 0 to 214 pCi/L, or 0 to 7,900 Bq/m³, at a resolution of 0.02 pCi/L.

The screen is E-Ink, which holds its image without power and is the main reason for the long battery life. It shows radon, the averaging period, temperature, relative humidity, battery level and a colored threshold bar. The sensor also measures atmospheric pressure, but only the app shows it. Radon can be shown in pCi/L, which Aranet calls the US standard unit, or in Bq/m³.

Bluetooth links the sensor to the free Aranet Home app for history, trends and alerts. The device keeps 30 days of history for the app to collect, so the record survives if the phone is away for a few weeks. No account or registration is needed, and the sensor works on its own without the app; most settings, including the threshold colors, are changed in the app, while units, the buzzer, Bluetooth and a reset are on the device's own menu. An icon on the screen shows when the buzzer is switched on, and it can also be set in the Aranet Home app, where Aranet says that with the buzzer on the device beeps each time a measurement is over the radon limit, 300 Bq/m³ (8.1 pCi/L) by default, so it works as an alarm; the warning thresholds can be changed in the app's advanced settings.

One long-term effect is spelled out in the datasheet. Like every ionization chamber radon detector, it slowly collects long-lived decay products such as lead-210 inside the chamber, which add counts even without radon. Aranet's own example: five years of continuous exposure at about 27 pCi/L (1,000 Bq/m³) could shift readings upward by around 4 pCi/L (150 Bq/m³). At ordinary household levels the effect is far smaller.