écouter aux portes, écouter en cachette
Tom is eavesdropping.
Tom écoute aux portes.
Avez-vous écouté aux portes ?
— The Lord of the Rings: The Fellowship of the Ring (2001)
Hey, boy, are you eavesdropping on them?
Hé, gamin, tu les écoutes aux portes ?
— A Silent Voice: The Movie (2016)