A method of controlling a wearable device worn on a finger of a user, includes: sensing a contact by a second finger of the user via an outer surface electrode located on an outer circumferential surface of the wearable device worn on a first finger of the user; based on the sensing of the contact, measuring an impedance between the outer surface electrode and an inner surface electrode that is in contact with the first finger of the user; identifying a type of the second finger based on the impedance; and controlling an operation of the wearable device based on the type of the second finger.