Some blind people can sense the shapes around them by listening to echoes from mouth clicks. It is similar to what bats do.
Wikipedia : Human echolocation
This is very useful, but unfortunately only a few are able to do this well.
I tried this myself, and discovered that it actually works. I was able to hear the shapes of big rocks and trees, and got a very clear sense of depth, while the image part of the echo was quite blurry. It is like they say: It is similar to a short blink with a dim flashlight on a dark night.
The main problems were:
1. Making a good sound for echoes.
2. The sound masking its own echoes, drowning them out.
So I took my inspiration from bats, which have lots of weird shapes on their faces which help against these problems. And I put in a loudspeaker for better clicky sounds. Moving it away from the ears works even better.
And my invention also works quite well when placed on the face with the mouth poking through the hole, making clicky sounds. That looks strange, but might be an advantage, since it makes it easy to recognize blind people wearing something like that on their face.
You may contact me politely: