This is just a weekend project I decided to make just because I wanted to prove how easily it could be done. The idea of course came from Hollywood where all the rich people often seem to have installed clap switches.
As explained in the video, this is accomplished using two opamps, one as a comparator and one to amplify the electret microphone signals. There is also a cap in series and a resistor in parallel to ground in order to detect and hold the peaks. The comparator outputs a nice square wave which makes it heaps easier to process the signals in the microcontroller.
Anyway, if anyone has further question feel free to ask them and I will answer them in the comments field.