Monitoring Radon Gas Levels

Automatically measuring and graphing Radon levels with an inexpensive device
Copyright 2012, Chris Nafis

Table of Contents


Radon is a radioactive gas. It comes from the natural breakdown of uranium in soil, rock and water and gets into the air we breathe. Radon can be found all over the U.S. It can get into any type of building and result in a high indoor radon level. It typically moves up through the ground to the air above and into your home through cracks and other holes in the foundation. Your home traps radon inside, where it can build up.

The average indoor radon level is estimated to be about 1.3 pCi/L, and about 0.4 pCi/L of radon is normally found in the outside air. The U.S. Congress has set a long-term goal that indoor radon levels be no more than outdoor levels. While this goal is not yet technologically achievable in all cases, most homes today can be reduced to 2 pCi/L or below.

See A Citizen's Guide to Radon for additional information. Also check out the EPA Radon site.


EPA Recommends the Following Testing Steps:

Step 1. Take a short-term test. If your result is 4 pCi/L or higher take a follow-up test (Step 2) to be sure.
Step 2. Follow up with either a long-term test or a second short-term test:
Step 3. If you followed up with a long-term test: Fix your home if your long-term test result is 4 pCi/L or more. If you followed up with a second short-term test: The higher your short-term results, the more certain you can be that you should fix your home. Consider fixing your home if the average of your first and second test is 4 pCi/L or higher.

Short Term Radon Test Kits

You can purchase charcoal test kits that you ship to a lab to analyze. They measure radon over a period of 48 hours. Since radon levels fluctuate, the results many not be representative of the true long term average levels.

Long Term Radon Test Kits

Long Term test kits measure radon levels for periods typically greater than 90 days. This particular alpha particle tracker uses foil to record the track of alpha particles that strike the foil.

Radon Gas Detectors

Radon levels vary in location and time, it is nice to have a monitor. Family Safety Products, Inc. manufactures the Pro Series 3 Radon Gas Detector . It is designed for use by the homeowner and has and easy-to-read LED display.


Back in 1999 I added an addition on my house. I forgot about the previous Radon problem I had with my 1833 Greek Revival house with it's dirt basement floor. In the 1980's I had put down plastic and poured concrete to eliminate the 16 pCi/L readings. In 2002 I ended up sealing the crack around the addition's floating basement slab, sealing the sump pit, and installing a radon fan. At the time I purchased a Safety Siron Radon Gas detector (model HS80002). My Long-Term reading has been around 2 pCi/L for years. Occasionally the Short-Term reading would approach 4 pCi/L. The readings always seem higher in the winter or when it rains hard. Since I have been building weatherstations and posting the data to the Internet , I thought it would be interesting to capture the radon information and try to correlate it.

Prototype 1: Using the Safety Siren Radon Gas Detector Model No: HS80002

WARNING: Removal of cover will void the warranty.

I have been a fan of the Rabbit Semiconductor processors, but I decided to learn about what the Open Source Hardware Arduino could do. I thought trying to post the Short-Term/Long-Term radon readings from my old Radon Gas detector to the Internet would be a great project. I'm always looking for good projects to work with the Schools on.

On the HS80002 unit, the AC plug is integrated into the PCB. Since I didn't want to ruin the unit, I decided to take a brute force approach to hacking it. There is easy access to the 2 digit LED when you take the cover off. I was still able to find the data sheet for the LED! Using a scope, I was able to find the two digit strobe signals. Then by looking at the LED display and the strobe signal I was able to deduce segments A-G.

Digit Strobes Segment signal

Ground Wire Digit / Segment Pins

Pushing the Long-term/Short-term switch momentarily will toggle the display between Long-term and Short-term Radon readings. The LED display alternates between showing which mode is selected and the Radon reading. Initially I used clips to connect to the detector pins.

Arduino GND => Ground wire on top of board
Arduino 2   => Digit 1 strobe
Arduino 3   => Digit 2 strobe
Arduino 4   => LED Segment A
Arduino 5   => LED Segment B
Arduino 6   => LED Segment C
Arduino 7   => LED Segment D
Arduino 8   => LED Segment E
Arduino 9   => LED Segment F
Arduino A0  => LED Segment G

The Arduino 1.0 Sample code for Safe Siren Radon Gas Detector Model HS80002 shows how it is relatively easy to create text with the radon value. This can then be used by a more complex Sketch to post the information to a data collection site like Arduino 1.0 has several example sketches under File => Examples => Ethernet such as PachubeClientString.

Prototype 2: Using the Safety Siren Pro Series 3 Radon Gas Detector Model No: HS71512

WARNING: Removal of cover will void the warranty.

I wanted to get another Safety Siren Radon detector so I could put one down in the basement and leave another one on the first floor where we spend most of our time in the house. When I went to purchase another Safety Siren Radon Detectors, I could only find a newer model (HS71512). There are several differences. The display now has four 7-segment LEDs and it reports in 0.1 pCi/L. The mode is now displayed with two LEDs.

I decided to add more functionality with the interface to the HS71512. I wanted to record both the long and short term Radon readings and I wanted to be able to control my Radon fan. Currently my fan runs 24x7x365 and draws around 120 watts. It keeps 0.75 WC Static Pressure according to my meter. I don't know how many CFM it is. Newer Radon fans that run 81 CFM at 1" WC Static Pressure say they take 60-95 watts. There is no safe level of Radon, but my long-term background reading stays around 2pCi/L. I want to run some experiments to see how much electricity I can save if I only turn on the fan when the radon readings are greater than my background level.

Arduino GND => GND
Arduino A0  => Digit 4 strobe
Arduino A1  => Digit 3 strobe
Arduino A2  => Digit 2 strobe
Arduino A3  => Digit 1 strobe
Arduion A4  => Long Term Strobe
Arduino A5  => Menu Button control
Arduino 2   => LED Segment A
Arduino 3   => LED Segment B
Arduino 4   => LED Segment C
Arduino 5   => LED Segment D
Arduino 6   => LED Segment E
Arduino 7   => LED Segment F
Arduino 8   => LED Segment G
Arduion 9   => Radon Fan Control

The transistor, diode, resister, and relay are used to "push" the menu button. Sparkfun has a nice discussion of how to use a relay. The Powerswitch Tail is used to control the radon ventilation fan. It draws it's power from the AC and only requires several ma at 5VDC to control.


Here are the materials that I used to develop this project. Most items are available from multiple vendors ( Adafruit, Sparkfun, Parallax, Acroname, Seeedstudio )


Other types of real-time data have sites that users can share their data with the global Internet Community. For example, Weather Underground is a great place to store my weatherstation data. StrikeStar is wonderful for processing distributed lightning detectors data to produce real-time maps.

Pachube ("patch-bay") connects people to devices, applications, and the Internet of Things. As a web-based service built to manage the world's real-time data, Pachube gives people the power to share, collaborate, and make use of information generated from the world around them.

This is a perfect repository for our Radon data. It provides a simple HTTP interface to post data and applications which generate charts that can be included on your web pages:

Notifying The User

Another great feature is that you can create triggers that can send alert messages to either your cell phone via SMS or to Twitter.

SMS Phone Text Messages

Twitter Tweets


Build your Own


Radon and Mitigation Information


This project is for experimental use only. The user assumes all responsibilities for assembly, installation, and use. This circuit is provided without warranty and the author makes no claim that this device will work in any particular application. Do not use in applications where failure or incorrect operation could jeopardize someone's safety. This schematic is provided for noncommercial use only.