A microphone with an electret microphone module. You can find the circuit diagram at http://ameblo.jp/shin-aiai/entry-12120744691.html.
In the article, the author suggests to replace the Zener diode with a resistor to reduce the noise. When one starts to replace the parts, he may also be tempted to replace the whole circuit, and the microphone module, and finally there will be no original parts at all.