was eavesdropping, was listening in
You were eavesdropping.
Они думали, что я сплю, а я все подслушивал.
They thought I was sleeping, but I was eavesdropping.
— Замри-умри-воскресни! (1990)
Если кто-то подслушивал, он узнал бы все.
If anyone had been eavesdropping, they would have found out everything.
— Славные парни (1990)