A Shabbat microphone is a non-electrical sound augmentation system that uses acousto-fluidic technology to allow Rabbis or Hazzans to amplify and transmit their voice without affecting the electrical current of the microphone in order to hold congregations without breaching laws set out in the Halakha regarding Shabbat. Rabbis disagree about whether even a Shabbat microphone can be used when the sound is being recorded.
References
Shabbat microphone Wikipedia(Text) CC BY-SA