Physics. Do the walls really have ears?

A friend of mine was just talking about a Physics lecture she went to. They said that some paint has metal filaments that pick up sound. This includes specific sound. So by analyzing the paint in a room you can actually pick out phrases said in that room. They also said this is a method the CIA uses on occasion, analyzing the paint for such things.

So my question is, have you heard of this?
Any information I can read on it?
It sounds surreal, I don’t want to ask “Is it true?” because this was a very reliable friend who was talking about the subject but that question does cross my mind.