What is the meaning of Doorbell?

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.

A button that activates an electric doorbell.

To ring many doorbells in an effort to contact people and thereby spread information or solicit.

To ring many doorbells of (target people or an area) in an effort to contact people and thereby spread information or solicit.

Source: wiktionary.org