That's what FDR did to ensure that Americans didn't remove gold from their safety deposit boxes -- government agents reportedly monitored what US citizens added or removed from their safety deposit boxes.
I've posted this in other threads, but it is appropriate here as to how far they will go.
Two brothers either got wind of FDR's coming devaluation or could figure it out for themselves. In any event, the converted $20,000 worth of gold notes into coin.
SIX MONTHS later, the feds tracked them down, took the gold and gave them $20,000 in paper. They took the case all the way to the Supreme Court, who said that there was no wrongdoing doing since they got their $20,000 back.