doorbell

Short definition from Wiktionary

Noun

1. 1
   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.
2. 2
   A button that activates an electric doorbell.

Verb

1. 1
   To ring many doorbells in an effort to contact people and thereby spread information or solicit.
2. 2
   To ring many doorbells of (target people or an area) in an effort to contact people and thereby spread information or solicit.