* After the Fukushima disaster, I learned that the only radiation monitoring numbers I could get (and they meant nothing to me) came from an EPA station over 100 miles away with months-long delayed analysis --and their air sampling wasn't working at the time. I bought an RD-1503 through Amazon.com and have logged an average of 5 cycled readings a day ever since.
* I've had no problems with my 1503, but I've read that a lot of handling can loosen up a critical solder connection inside, so treat it nice. Don't let it get contaminated, wet, or even very humid.
* The best way to use this instrument is to pretty much keep it at home, protected inside a small, thin, resealable plastic sandwich bag. Do your monitoring in the same way, at the same location, and at about the same time of day --so that you have a meaningful "base line" of readings for comparison. You want to methodically do 5 "background" readings and average the results, then subtract that average from 5 readings on anything special.
* Don't be fooled by radon\daughters, which decay by half (always first subtracting background) in about 40 minutes. Radon is _bad_ stuff, I chart it, and I wonder about its comings and goings, but it's probably not coming from Japan. However, should your background readings take a big and sustained jump, or if you get a sample of something that keeps reading high the next day, you may have identified a problem.
* Learn about your instrument's limitations. It's very hard to usefully read beta emitters in food, water or milk with any Geiger counter. That takes trained personnel, special procedures and expensive spectrometry equipment in a lab.
Google "Radex-RD1503" + "SW Oregon" for the little bit I've managed to learn.