prisluškivati

1. to eavesdrop; to listen in
   Nemoj da prisluškuješ kad odrasli razgovaraju! — Don't eavesdrop when the grown-ups are talking!
   Komšinica stalno prisluškuje iza vrata. — The neighbour is always listening in behind the door.
2. (with devices) to tap; to bug
   Policija je mesecima prisluškivala njegov telefon. — The police tapped his phone for months.

Used with an accusative object (prisluškivati razgovor, telefon) or without one.