The document discusses silent sound technology, which allows communication without speaking aloud. It originated from the idea of interpreting silent speech electronically. The technology uses electromyography to monitor muscle movements when speaking and converts them to electrical signals representing speech. Image processing also analyzes lip movements. Some applications include helping people who lost their voice and covert military communication. The technology could enable silent phone calls and transmitting PIN numbers securely. Overall, silent sound technology implements "talking without talking" and may have useful applications in the future.