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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.