MB3 184a: Using a Door Knocker on Shabbos (338:1)

Knocking on a door and vocal singing are permissible on Shabbos. Using a door knocker on Shabbos. Opening a door that has a bell on it.

Moving toys that make noise on Shabbos.

Using a microphone on Shabbos and אוושא מילתא.

Bells on a parochet or on a Sefer Torah.