You can use your hands to scroll on your screen, play music and do all sorts of crazy things thanks to this Doppler effect experiment right now.
Put together by developer Daniel Rapp, he codes an entire webpage that allows people to utilise the doppler effect to wirelessly control your computers.
According to Gizmodo on the physics behind it:
“The technique is reasonably simple: an inaudible, high-frequency tone is emitted by your speakers. When the soundwave reflects off moving object (read: your hand), it’s frequency-shifted, a shift which is measured using the microphone, and interpreted as a gesture by the computer.”
So basically your microphone is more powerful than you would ever think.
Check out his website for the experiment: Daniel Rapp