Ask HN: Is there any “phantom” keyboard?

A keyboard which is just a camera (or sensors), visually determining hand positions to register keystrokes. Is there any such thing?

I’m aware of Tactual Labs (https://vimeo.com/258421095) but I can’t afford that, and I’d like my keyboard to be something I can carry in my pocket (a phantom keyboard, as I described.)

There’s a damn amount of unexplored productivity potential in this area, especially considering 3d gestures and such.

If there isn’t any, I may build one.