annunciator

noun4

1. •
   Anything that announces something.
2. •
   An officer in the church of Constantinople, whose business it was to inform the people of the festivals to be celebrated.
3. •
   A signalling device that shows which of several electrical circuits is active, especially such a device in a telephone switchboard.
4. •
   (UK) A buzzer in a signal box that sounds when a train activates a treadle positioned on the track, and thus provides a warning or announcement of a nearby train.