Reversing itself, the Defense Department says an espionage report it produced that warned about Canadian coins with tiny radio-frequency transmitters was not true.
The Defense Security Service said it never could substantiate its own published claims about the mysterious coins. ....
The service had contended since late June that such 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.
....Experts said such tiny transmitters almost certainly would have limited range to communicate with sensors no more than a few feet away, such as ones hidden inside a doorway. The metal coins also would interfere with any signals emitted, they said.
Experts also warned that hiding tracking technology inside coins would be fraught with risks because the spy's target might inadvertently give away the coin or spend it.