Radon alarms: detectors that sound, and system alarms

A smoke or carbon monoxide alarm warns of danger in minutes. Radon is different: the EPA's guidance is to fix a home with a radon level of 4 pCi/L or more and to consider fixing between 2 and 4 pCi/L, and that guidance is about the level over time, not a single hour. C-NRPP's advice for any consumer monitor is to test for at least 3 months, preferably in the heating season, and to decide on the long-term average.

That is why detector alarms are built on averages. Kidde's RAB, for example, sounds once the average radon concentration over the past day has exceeded its threshold, not on a single reading, and Kidde's guide notes that because radon decay is random, two units can read slightly differently and an average over 7 days or more is the better reference. Indoor radon also changes between day and night, so a single alarm is a reason to keep watching and to look at the long-term average, not a reason to leave the house.

These are the detectors we cover whose makers state an audible alarm. Each maker describes its alarm differently, so the table keeps to what each one says: whether you can set the level, how the alarm sounds, and how you silence it. Where a maker does not state something, the table says so rather than guessing.

Two practical differences stand out. The Airthereal and GQ models, the FD-65-RADON, the AEGTEST HOUND-3699 and the Ecosense EcoBlu, EcoQube Flex, EcoTracker and RadonEye Pro let you choose the level, which matters if you want a warning below 4 pCi/L, inside the EPA's consider-fixing range. And the battery models can sit in any room without an outlet: the Aranet Radon One and Radon Plus, the EcoQube Flex, Kidde RAB and XR0B-SR on disposable cells, and the Airthereal RM-63Pro and RM-65, the FD-65-RADON and the AEGTEST HOUND-1011, HOUND-1011S, HOUND-1085, HOUND-3699 and HOUND-3786 on rechargeable ones. For the HOUND-3699, AEGTEST's current store lists a charging data cable and the battery is in its earlier store's listing. The PYZYCKYH RD17 plugs into a wall outlet or runs from its built-in rechargeable battery. The EcoBlu, EcoTracker, RD200 and SafetySiren Pro4 plug in, the RadonEye Pro runs from a 12-volt adapter or a battery pack, and the three GQ models run on USB power without batteries. The Pro4's alarm level is preset by the manufacturer for the model you buy, and PYZYCKYH does not say what level sets off the RD17's alert. X-Sense also lets you switch the XR0B-SR's audio and visual indicators off in its settings, and its alarm clears on its own once the level drops. Aranet's buzzer is switched on or off on the device or in its app, and the Radon One's buzzer ships switched off; Aranet says its threshold bars can be changed in the app but does not say which level sounds the buzzer.

These detectors take time to settle. Kidde says the RAB's first reading takes 12 hours, X-Sense gives 4 to 24 hours for the XR0B-SR's first reading, Airthereal gives 6 hours for the RM-65's first data and Forensics Detectors 6 hours for the FD-65-RADON's first measurement, PYZYCKYH gives about 6 hours for the RD17's first radon reading and Family Safety Products 48 hours for the SafetySiren Pro4's. AEGTEST gives 6 hours for the first results of the HOUND-1011 and HOUND-1085, up to 12 hours for the HOUND-1011S, 1-hour detection for the HOUND-3699, and a first reading in 10 minutes with stable data within 1 hour for the HOUND-3786. GQ says its monitors show the background radon level within about 5 minutes of being switched on, the Ecosense monitors show a first reading within an hour or less, and Aranet says its two show a first measurement after 10 minutes and reach full accuracy after 1 hour, so an alarm in the first day says little.

Several monitors have no buzzer but still warn you. Airthings' Wave Radon glows green, yellow or red, and Airthings sets red at 4 pCi/L and above; its View Radon uses the same colors on its display, and Airthings says red means it may be time to seek advice from a radon mitigation professional. X-Sense's XR0A-iR connects over Wi-Fi to the X-SENSE Home Security app, which gives remote access to its readings and app notifications when you are away from it. SunRADON's lüft turns its front light yellow or red when any of its six sensors reaches a warning or alert threshold, which can be changed in its app, and sends alerts when levels rise past your limits. INKBIRD's INK-RD3 has no buzzer or app; INKBIRD describes an LED light and three-colour bars on the device, yellow from 2.7 pCi/L and red at 4 pCi/L and above. TurinSen's Hello Radon C lists no sound alarm or app either: a color-coded LED that flashes once per minute and a color-coded bar on its e-ink screen, with no levels given for the colors.

The other kind of radon alarm guards the fix, not the air. The EPA says a warning device must be installed to alert you if an active system stops working properly, and that it must be placed where it can be seen or heard easily. Its guide to radon-resistant construction adds that, unless the indicator is part of the fan's power supply, an audible or visual alarm should be on a separate circuit so it still works if the fan loses power.

The usual warning device is a manometer, a U-shaped tube on the vent pipe: Pennsylvania's guidance says the fan is running if the fluid levels on each side are uneven, and that even levels mean the fan may not be working or may be off. Minnesota goes further and requires every mitigation system to have two fan monitors: a U-tube manometer and an active notification monitor that alerts you with a light or a sound if the system stops working, with the installed manometer reading written on a sticker beside it.

Active notification monitor

A device that senses the suction in a radon system's pipe and lights up or sounds when it drops, so a stopped fan does not go unnoticed. Fantech's radon alarm, for example, mounts directly on 3, 4 or 6-inch PVC pipe, gives a visual and audible alert with a low-battery warning, and lets the installer set a 24 or 96-hour delay; Fantech lists its pressure limits as 0.04 to 10 inches of water column.

1. 1Step 1 of 4:

   Check the warning device

   The EPA says to look at your warning device, usually a manometer, regularly to make sure the system is working.

2. 2Step 2 of 4:

   Know the installed reading

   Where the installer wrote the manometer reading on a sticker, compare against it; even fluid levels mean the fan may be off.

3. 3Step 3 of 4:

   Keep the fan on

   The EPA says the fan should never be turned off; it must run continuously for the system to work.

4. 4Step 4 of 4:

   Retest anyway

   The EPA suggests retesting at least every two years, alarm or no alarm.

If a detector's alarm sounds, look at its averages rather than its latest reading, and give it time: a single high day is not a long-term level. If the long-term average is 4 pCi/L or more, the EPA's guidance is to fix the home; between 2 and 4 pCi/L, it says to consider fixing. Find a certified installer in radon mitigation professionals, and read your number with the radon level interpreter.

If a system alarm sounds, the fan has most likely stopped or lost suction. Check that it has power, then call the installer; the EPA notes fans may last five years or more, and manufacturer warranties tend not to exceed five years. Until it runs again, the system is not reducing radon. The fans themselves are compared on radon fan models, and every monitor we cover is on radon detectors and monitors.