SB Nation made this video on the history of the radio in the quarterback’s ear. The Chiefs have their own history of this but from the other side as the Arrowhead crowd noise tries to make it difficult for the opposing quarterback to hear the calls on his radio. You can see some quarterbacks putting their hands over the helmet like they’re trying to hear.
The radio wasn’t allowed for a while then it was allowed again. Warren Moon, Brian Billick, Trent Dilfer and others talk about it. Interesting stuff.