During the final battle scene, there are several moments when Captain America comminicates with Iron Man and/or Black Widow from a great distance away. Presumably, Cap is using a radio, and usually raises his hand near his ear as if indicating he's using an earpiece of some kind. Problem is, there's no earpiece to be seen! Widow, Nick Fury, Hawkeye, Maria Hill & everyone else can be seen using a blue tooth like device. But not Cap. And during this time, his cowell is off, so it can't be that he has one hidden there.