(one) could hear a pin drop

One could perceive the tiniest noise because the room is completely quiet and still. We all stayed so quiet following the boss's outburst that we could hear a pin drop. Sarah said she could hear a pin drop as the audience intently watched the actors on stage. You could hear a pin drop after Grandpa's dentures fell out of his mouth in the middle of Thanksgiving dinner.

hear a pin drop, one/you could

Complete silence. This hyperbole dates from the early nineteenth century. An early appearance in print is in Susan Ferrier’s The Inheritance (1824): “You might have heard a pin drop in the house while that was going on.” Although pins are a far less common household item than they once were, the expression survives.