Did you know that the dust that's in the air and settling all over your house (and computer monitor) is radioactive? It's true, it contains radioactive decay products from naturally occuring Uranium and Thorium.
As an experiment, I wiped some dust from the TV screen onto a tissue, and placed it in front of the radiation detector. The reading went from a background reading around 10 CPM to around 1300 CPM, or 130 times the reading!
I was doing laundry one day, and decided to check out the lint that collects in the lint filter in the clothes dryer. It produced counts around 240 CPM, again much higher than the background readings. This is probably due to the numerous uranium/thorium atoms and daughter products that are floating in the air, which get stuck to your clothes, and are sucked into the dryer.
When you fly in an airplane, you're up above much of the Earth's atmosphere. It's the air that protects us from a lot of radiation due to cosmic rays coming from outer space. Recently I took a transcontinental flight, and of course a GM-10 Radiation Detector came along for the ride! The CPM (Counts Per Minute) went from about 12 on the ground to 360 in flight.