n A device on or adjacent to an outer door for announcing one's presence. It can be mechanical, directly sounding a bell, or a button that electrically sounds a chime or buzzer inside the building.
n A button that actives an electric doorbell.
v (intransitive) To ring many doorbells in an effort to contact people and thereby spread information or solicit.
v (transitive) To ring many doorbells of (target people or an area) in an effort to contact people and thereby spread information or solicit.