Tap Code Translator
Turn text into tap code and back: hear it knocked while the grid lights each row and column, or knock a message on the pad. The prisoner’s knock code, made simple.
Tap code
•• ••• • ••••• ••• • ••• • ••• ••••
| 1 | 2 | 3 | 4 | 5 | |
|---|---|---|---|---|---|
| 1 | A | B | C/K | D | E |
| 2 | F | G | H | I | J |
| 3 | L | M | N | O | P |
| 4 | Q | R | S | T | U |
| 5 | V | W | X | Y | Z |
Knock a message
Tap the row, pause, tap the column, pause. Each pair makes a letter.
Your knocks appear here
How it works
Every letter is a square on a 5 by 5 grid. Knock its row, pause, then knock its column.
Find the row
H is in row 2 (F G H I J), so knock twice.
Find the column
H is third along, so pause and knock three times.
Next letter
A longer pause ends the letter. HI is •• ••• / •• ••••.
Prisoners of war in Vietnam’s Hoa Lo prison tapped news, names and courage through cell walls this way for years.
Tips
- Learn the gridRows start A, F, L, Q, V. Remember those five and you can find any letter.
- Knock itOn the pad, knock the row, pause, knock the column, pause. Each pair is one letter.
- ListenKnock it plays the message with a short gap inside a letter and a longer one between letters.
- Not a cipherAnyone who knows the grid can read it, so it hides nothing: it was made to be easy to learn in secret.
Frequently asked questions
About the tap code translator
A way to send letters as knocks on a 5 by 5 grid of the alphabet. Each letter is two groups of knocks: its row, then its column. It is also called knock code.
Twenty-five squares fit twenty-six letters only if one doubles up, so C stands in for K. Read “C” as K when the word needs it.
American prisoners of war in Vietnam made it famous, tapping on cell walls. It goes back to a Polybius square, and Russian prisoners used a version in the 1800s.
Tap code needs only one kind of sound, a knock, so it works through a wall where long and short sounds are hard to tell apart. It is slower than Morse but easier to learn.