Oh, as you all know, I spent a great deal of time in the nuclear forensics field. Something the average (and not so average) person doesn't know, the air filter in your car and in your vacuum cleaner is one of the most radioactive things you will ever touch (assuming you're not a RAD worker). The entire planet is lightly coated with heavy metals from all the nuclear testing we've done over the years, and our air filtering devices actually concentrate this dust. It's always interesting to take a meter with decent sensitivity and test an air filter for radiation...
I would imagine this is particularly fun in Hiroshima and Nagasaki.