How do you turn an ordinary wall into a piano?
There are two microphones attached on the wall surface. Those microphones are acting like human ears for the computer which is able to “hear” as people tap/bang on the wall. The program translates those hits into piano keys. It all depends on how hard you hit the wall. The lower key will be produced when you hit it harder and the higher key will be produced when you hit it softer. Just like every other modern piano, it has 88 keys.
You have to see the video - it’s pretty cool