Understanding Your Radon Alarm: What It Tells You and When to Act

If you live in St. Louis and you have a radon mitigation system, you have probably seen a small device mounted on a wall or sitting on a shelf that beeps or flashes when radon levels rise. That device is your radon alarm. It is not a decoration. It is a tool that tells you when something has changed in your home's radon mitigation system, and it deserves your attention.

I have worked on radon systems for years, often arriving at a home after the homeowner has heard that alarm go off. By the time I get there, the radon alarm has been sounding for days or weeks. People wonder: is it a false alarm? Do I need to call someone? How urgent is this? The short answer is that a radon alarm is designed to get your attention for a reason. The longer answer involves understanding what your radon mitigation system does, what can go wrong, and what the alarm means for your family's health.

What Your Radon Alarm Is Actually Monitoring

Most residential radon alarms are continuous radon monitors. They sample the air in your home every hour or so and track the average radon level over time. When that average crosses a threshold - typically 4.0 picocuries per liter, the EPA action level - the alarm sounds. Some units give a visual warning like a flashing red light or a digital readout. Others emit a tone. Either way, the message is the same: your indoor radon level is higher than it should be.

The important thing to understand is that a radon alarm does not tell you why the level is high. It only tells you that it is high. The cause could be something simple, like a radon fan that has stopped working. It could be a crack in a radon vent pipe, or a blockage in the soil suction system. It could also be something unrelated to the system itself, like a new radon entry point that opened up after foundation work or soil settlement. The alarm is just the messenger. What you do next matters.

Common Reasons Your Radon Alarm Goes Off

Over the years, I have seen a handful of repeat offenders when it comes to false or real alarms. Here is what typically happens:

• Fan failure. The radon fan is the heart of a sub-slab depressurization system. If it stops spinning, the vacuum under your slab disappears and radon gas can seep back inside. The alarm will catch that rise within a day or two. Fan replacement is one of the most common repairs we do at Air Sense Environmental.
• Damaged or disconnected radon vent pipe. A pipe that gets knocked loose in the basement or a pipe that is cracked above ground can break the suction path. The system runs but does not pull radon from under the house.
• Changes in the home. Major remodeling, new windows, a new furnace that changes air pressure - any of these can alter how your home breathes and allow radon to enter more easily.
• Seasonal shifts. Radon levels are often higher in winter when homes are closed up and the stack effect pulls soil gas inside. A radon alarm may sound only during cold months, which is a sign that your system needs adjustment.

In each case, the alarm is doing its job. The question is whether the underlying issue is minor or something that needs a professional radon inspection.

When a Radon Alarm Means You Need Immediate Help

Some situations call for a quick response. If the alarm has been sounding for more than 48 hours and you have checked the obvious things - the fan is running, the pipe is intact, the unit is not unplugged - then you should call a radon mitigation system service provider. Prolonged exposure to elevated radon levels increases your risk of lung cancer. The EPA is clear that there is no safe level of radon, only acceptable risk.

I have walked into homes where the radon alarm had been chirping for two weeks. The homeowners assumed it was a glitch. When I tested the system, I found that the radon fan had failed completely. The radon level in the basement had climbed to over 12 pCi/L. That is three times the action level. Those families had been breathing elevated radon for weeks without knowing it.

If your radon alarm goes off and you are not sure what to do, the safest move is to run a home radon test with a radon test kit while you wait for a professional. That gives you a second data point and confirms whether the alarm is accurate. But do not ignore the alarm. Treat it like a smoke detector. If it beeps, you check it.

Radon Alarm Maintenance and Best Practices

Your radon alarm is a monitoring device, and like any device, it needs basic care. Here are a few things every homeowner should know:

• Keep the unit plugged in and away from drafts, direct sunlight, and high humidity. These conditions can mess with the sensor readings.
• Test the alarm function periodically. Most units have a test button. Press it once a month to confirm the display and sound still work.
• Replace the battery if your unit has a backup battery. Many continuous radon monitors have a small battery that keeps the clock and memory alive during power outages. A dead battery can cause the unit to reset or lose its calibration.
• Do not mount the alarm near a window or an exterior door. Outdoor air can dilute the sample and give a falsely low reading.

I also recommend having a radon mitigation system maintenance check every two to three years. A professional can inspect the radon fan, check the radon vent pipe for blockages or leaks, verify that the sub-slab depressurization is still pulling properly, and look for new radon entry points that may have developed. Crack sealing is often part of that process. Over time, concrete floors settle and new gaps open. If those gaps are not sealed, radon gas can bypass the system entirely.

Radon-Resistant Construction and Retrofits

If you are building a new home in St. Louis, radon-resistant construction is a smart investment. It involves installing a layer of gravel and a vapor barrier under the slab, running a radon vent pipe from that layer up through the roof, and sealing all major cracks and openings. Even if you do not install a radon fan right away, the passive system can be activated later if testing shows high levels. Many new homes in the area include this as a standard feature now.

For existing homes, retrofitting a sub-slab depressurization system is the most effective way to lower high radon levels. It creates a vacuum beneath the foundation, pulling radon gas away from the house and venting it safely above the roofline. That is the same type of system that your radon alarm is monitoring. When the system works correctly, the alarm stays quiet. When something breaks, the alarm speaks up.

Trusting Your Radon Alarm

I have seen people disable their radon alarm because they were tired of the noise. That is a mistake. The alarm is not the problem. The problem is the radon level. If you silence the alarm without fixing the cause, you are simply choosing not to know that you are breathing a known carcinogen.

At Air Sense Environmental, we spend a lot of time explaining to homeowners that their radon alarm is a health device, not a convenience feature. It belongs in the same category as a carbon monoxide detector or a smoke alarm. You would not ignore those. Do not ignore this one.

The next time your radon alarm goes off, take a breath. Check the display. Look at your radon mitigation system. If you cannot find the problem, call someone who can. A short-term home radon test can give you peace of mind while you wait. But whatever you do, do not assume it is nothing. In my experience, it is rarely nothing.