We'll have some interesting guests on tomorrow's show, so be sure to listen in. [=tune in]明天的节目里我们将邀请一些有趣的嘉宾，请注意收听。

They let me listen in when the plans were presented.他们让我旁听了方案的陈述。

Someone was listening in on our telephone conversation.有人在窃听我们的电话。