Tap Code: Encode and Decode Online The Tap Code is a code (similar to Morse code), commonly used by prisoners in jail to communicate with one another. The method of communicating is usually by "tapping" either the metal bars or the walls inside the cell, hence also called knock code. It is a very simple code, not meant to avoid interception, since the messages are sent in clear text. Use the above Tap code decoder and translator to encrypt/decrypt simple messages. If this tool was helpful, tweet it or share it.