I saw this on the net today and I think it’s a great idea. Personally I use Morse code, But this limits me in two ways. 1. I need a electronic medium to transmit over great distances. 2. The person receiving the message needs to know Morse code. With his you could easily use a light or any noise maker. Here is the Wikipedia page on it. https://en.wikipedia.org/wiki/Tap_code Here is…