CONTINUOUS RADON MONITORS
Charcoal kits are "short-term, passive test devices" because the data they obtain must be analyzed in a laboratory off-site. On the other hand, continuous radon monitors are considered to be "short term ACTIVE devices" because they are electrically powered (by AC current or lithium batteries) and take REAL TIME hourly averages. They also usually provide a "full test average" upon test termination. Note: some electronic radon monitors (sold over the Internet) provide an "average" of for the test. One unit even displays the radon level hourly on its LED screen. However, these devices do NOT "collect" these hour-by-hour" readings and allow them to be printed out at the termination of the test. This is WHY they have never been "approved" in our industry as analytical test devices which can be utilized for "real estate transactions"
Furthermore, if the more expensive continuous monitors must be "re-calibrated" annually by the device manufacturer there is good reason to be concerned about the "accuracy" of a device costing less than $200.00. With such devices how would you ever KNOW if they were operating properly? It is especially critical when your health is at stake to have "good information". We have even found that some homeowners like purchasing these units so they can see an "digital readout" of their radon levels. But the latin phrase "Caveat Emptor" also applies...."Let the buyer beware"!
The BEST answer in obtaining valid radon results is to hire a certifical professional with "analytical" qualifications!
To obtain an hourly average, a continuous monitor takes multiple radon samples (counts) during each hour. The more "counts" a monitor takes the more "sensitive" it is and the more accurate the results will be. Its analogus to a student who takes a test in school. The more tests they take in a semester the more "representative picture" you get of the kind of student they are.
Having an hourly record of what actually took place in the house during the test is crucial for the "radon test professional" to make a qualified assessment as to whether the test numbers obtained were valid. Obviously, part of being "certiifed" to conduct radon testing means that you agree to follow all proper EPA radon testing protocols to ensure the probability of a good test. But there are other features that some of the better continuous radon monitors provide which aid in assessing whether "test tampering" occured.
In addition to hourly radon results, several brands record hourly readings for temparature, barometric pressure and humbidity. Looking at all this data "collectively" the certified test professional can make a determination of test validity. Some monitors have built in "motion detectors" which detect whether the device has been "picked up and moved". Several monitors are operated by AC power, while some come with built-in lithium batteries that operate even if power to the house is temporarily interrupted by "surges" or "loss of power". Loss of electricity during a test for AC power based units would generally mandate that a "re-test" be performed because the test professional has no way to know how long the power loss went for or whether tampering was done during that time period. Lithium battery based units help ensure that test results are readily available for real estate closings.
To be "qualifed" to deploy and interpret the test data from a continuous monitor a radon professional should be certified to perform "standard AND analytical" test services. To be listed for analytical services, you must send your radon monitor to a radon laboratory where they exposure it to a "given level" of radon. When its returned to you, you have to be able to tell them the exact amount of radon that was captured by the monitor. Doing so demonstrates that you are "proficient" to operate that device effectively. Most home inspectors who are certified to radon testing are only certified to perform "standard" testing services (charcoal kits). Make SURE that your radon testing source can provide a photo ID badge from their national certification organization which documents their testing qualifications. If you are paying good money for a radon test, is this too much to ask?
So as you can see....there is MORE to radon testing with continuous monitors than simply "plugging it into a wall receptacle"