*Note - In the interest of full disclosure: We currently have this item for sale and the following is the description in the listing. We are using it today because it's been a very busy weekend and we have nothing else to bring to the table. Besides, it's a rather fun item, in an odd sort of way!
Everyone should have one of these near the entrance to the fallout shelter so you can seal yourself in on a moment's notice! I'm, (sadly), old enough to have actually been in a fallout shelter as a very young child. Someone down the block built one and we had a brief tour. All I recall is that there was lots of concrete and it was rather dark and dismal.
This is the nu-klear Fallout Detector made by Minutemen Industries Inc, Chicago Ill. It's made of plastic and measures about 3 3/4" across and 2 1/2" tall. The directions on top instruct "Shake Gently Until Some Beads Float, Seek Shelter at Once if All Beads Drop, Remain In Shelter Until Some Beads Float". (Terrifying, don't you think?: "DAD, DAD...the beads all dropped!" "QUICK KIDS - GET TO THE SHELTER!!!")
I'm happy to report that shaking the device causes some of the beads to cling to the side of the sphere rather than falling like dead ducks; we are, for the moment safe from radiation here in the sunroom.
For further info on this gadget read this excellent article posted by Oak Ridge Associated Universities