Door chime
A door chime or doorbell was an audio signal meant to indicate that a visitor was outside the door.

The door chime of the ancient Vulcan monastery at P'Jem consisted of a rope tied to a . Sub-commander T'Pol used it to announce the presence of the landing party from  in 2151. ()

Following the Battle of Azati Prime in early 2154, the door chime at Captain Jonathan Archer's ready room was non-operational, so visitors had to knock on the door to announce their presence. ()

In 2367, hallucinations brought on by lack of REM sleep caused Captain Jean-Luc Picard to repeatedly hear the chime for the door of his quarters. Each time, he answered with his standard response of "Come," until finally, growing irritated, he stated "Yes, yes," only to go to the door and find nobody there. Finally, after several more rings, he heard a knock upon the door and upon his statement of "Come," Beverly Crusher and Deanna Troi entered. ()

In 2369, Jake Sisko and Nog used the doorbell of Varis Sul's quarters aboard Deep Space 9 and waited until she let them enter. ()

When Doctor Julian Bashir had to use his emergency medical override authorization to enter Elim Garak's quarters aboard Deep Space 9, he found the Cardassian giving himself an injection. Garak, trying to talk this situation away, said that the doctor was a pleasant surprise and he must have missed the door chime. ()

In 2374, Tom Paris and B'Elanna Torres were interrupted during their romantic dinner by the door chime. Though Torres asked Paris to ignore it he opened the door to see Harry Kim. ()

External link 
 
Communications technology