Name it (Audio Detecter)

hello friends,

i'm in search of an audio senser/detecter..
i dont need to cheak the intensity but just want to cheak if there's change in level of audio..

i've seen a similar project..pics has been shown
when you clap it rotates in one direction and on other clap rotation reverses..

i want to know the name of the senser which is used in project..

thank you friends...