There are instructions available for a homemade fallout meter which is made using commonly available items. Although not as accurate as some of the newer digital meters, it is accurate enough that you would have a pretty good idea how much radiation you have been exposed to.
Directions: http://www.ki4u.com/free_book/s60p792.htm
Evaluation: http://74.125.95.132/search?q=cache:0RhPUA3lNlwJ:jtyson.bol.ucla.edu/documents/KFM.pdf+how+to+make+radiation+detector+ruler+aluminum+foil&cd=2&hl=en&ct=clnk&gl=us
Edit - directions also linked from this page: http://ballew.org/homeland/fallout.html
