Question

listen
  in

Accepted Answer

1(often with to) to listen to a radio broadcast:If you listen in tonight  you'll hear my brother talking about his new play.2 (often with on) to listen intentionally to a telephone conversation ,a message intended for someone else etc:It was impossible to discuss anything private over the telephone, as the operator was in the habit of listening in (on our converations).

Listen 1(often Radio Broadcast:If Tonight You'll Hear Brother Talking