Over at Make: Online, John Park posted this video of a gadget that generates random numbers by watching sand fall through an hourglass.
It watches falling sand in an hourglass with an optical sensor. That data is sent via the Arduino USB output to the PC where it's analyzed. This entropy is useful for all your random number needs. My favorite part: when the hourglass runs dry a servo motor flips it over and it starts again.USB Hourglass random number generator
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. Come and hear Mark speak at the ALA conference in Chicago on July 1.