The tiny electronic transmitter can use to monitor individual movement within certain parameter, but technologically it makes no sense, coins can be easily spent or given away. Quotes from the news,
“I think we can be pretty darn confident that the technology is there for the sorts of micro-units that would be required to embed these things in a coin”
“You could almost, by handing a coin to somebody, achieve the equivalent of the Mafiosi’s last kiss on the cheek.”
Dept of Defense spokesman also said coin could be use to identify special target.