WASHINGTON — Can the coins jingling in your pocket trace your movements?

The Defense Department is warning its American contractor employees about a new espionage threat seemingly straight from Hollywood: It discovered Canadian coins with tiny radio frequency transmitters hidden inside.

In a U.S. government report, it 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.

The U.S. report doesn’t suggest who might be tracking American defense contractors or why. It also doesn’t describe how the Pentagon discovered the ruse, how the transmitters might function or even which Canadian currency contained them.