Looking at this page makes me think that it's probably possible to detect that (not what) people are speaking or typing. I placed my phone on the surface. And

Looking at this page makes me think that it's probably possible to detect that (not what) people are speaking or typing. I placed my phone on the surface. And did see the numbers jank when I started typing. Then I left it at rest and said a loud "Booo!" and saw the numbers jump again. To confirm, I'd need to plot the numbers and do some statistical analysis, which is far too much work for me now :D