Hollow coin to transfer messages between borders, between lovers, and between betweens. Oh boy. Jan. 11, 2007: The U.S. issues a spy coin warning after discovering tiny transmitters planted in Canadian coins...tiny transmitters found on contractors with classified security clearances. The government said the mysterious coins were found planted on U.S. contractors with classified security clearances on at least three separate occasions between October 2005 and January 2006 as the contractors traveled through Canada. Don't you love a thrill? What are the Canadians up to? Naughty! Easy to use and plant. To open, place in the metal ring face up, tap on the table hard, 3-4 times. You'll get the trick. Two metal coin-opener rings are included.