EPA test Protocols - "Protocols for Radon and Radon Decay Product Measurements in Homes" by the EPA is supposed to guide all home radon testing. But at 47 pages, it's rarely read. We edited it to 4 pages that Realtors and home inspectors should commit to memory.

You'll find both the full and condensed versions under "Publications."

Short term testing - A short term test runs 2 to 90 days, depending on the device.  All short term testers will give you a very accurate reading, but only of a short window of time.  Although the radon levels in most homes will vary by perhaps 10% to 20% depending on the weather and the season, a small number of homes will have significant variations.  So if you have time, it’s usually best to do a long term test.

Long term testing - A long term test runs 3 to 12 months, and gives the best picture of your real radon exposure.  Many people start with a short term test, and if the results are marginal, follow up with a long term test.

Test types - Continuous electronic monitors are usually requested by home buyers because they are very hard to tamper with.  They must be operated by trained professionals.
Charcoal tests are the most common form of testing because they are cheap, accurate and simple enough for anyone to do.  Most people place two units side by side in their basement. Minnesota residents can order discount priced charcoal tests from Aircheck.
Alpha track is the most common long term tester. It is also very simple.  It is best to deploy it over multiple seasons, with some heating, some cooling and some open windows. Minnesota residents can order discount priced alpha tracks from Aircheck.
E Perms are reusable and are usually deployed by public health departments.  They can be used short or long term.

Home owner testing - All tests
• Put the test unit in the lowest usable level of the home, in an area that is regularly used.
• Put the test unit away from drafts, high heat, direct sun and high humidity.
• Put the test unit 2’ to 7’ from the floor, at least 1’ from exterior walls, at least 3’ from exterior doors or windows and at least 4” from other objects.
• Do not put the test unit in kitchens, bathrooms, laundry rooms, furnace rooms, closets, porches or crawl spaces.
• Do not put the test unit near sump holes or floor drains.
Short term tests
• Do not test during severe storms, if winds exceed 30 mph or if the barometric pressure is rapidly changing.
• Except for normal traffic, keep doors and windows closed for 12 hours before the test and during the test.
• Do not use whole house fans or fireplaces.
• Room air conditioners must recirculate the room air, not exhaust it .
• The furnace, central air and air exchanger (HRV) should be running normally.

Home sale testing
• A professional tester should apply tamper detecting strips to basement doors and windows and tell the occupants what they can and can’t do during the test.
• Follow the same guidelines as for home owner testing, except the test unit should be put in the lowest level that has a concrete floor and could be finished.
• For charcoal tests, the EPA requires the use of 2 units in the same location, either simultaneously or sequentially.