Who is going to fund a company whose business model involves making people hear mysterious voices from on high? Well, I suppose angel investors might.

Just replace the creepy voices with ads and watch the money roll in.

In college, some friends and I tried to build a detection system that would predict conversation lulls in public spaces - like when you're in a restaurant and it randomly gets quiet - so we could insert premium audio ads at those moments.

We never got it working, but when I see stuff like this sometimes I still think about it.