How do you send morse code by blinking?
By holding each blink for the length of its mark. Close your eyes for one count for a dit and three counts for a dah, open them for one count between marks, three between letters and seven between words. Keep the counts even, because the lengths are the whole message.
... --- ...
The flashlight needs camera access. Nothing is recorded or sent.
Three short, three long, three short. Play it and watch the lamp: that on and off pattern is exactly what your eyes have to copy.
The rhythm is the same, the switch is different
Morse does not care what produces the signal. ITU-R M.1677-1 fixes the lengths, not the medium, so a tone, a lamp, a vibration and a pair of eyelids all carry the same code as long as the ratios hold.
Eyes closed is the signal being on. Eyes open is the signal being off. That gives you the four lengths you need:
- a dit is one count with your eyes closed
- a dah is three counts closed
- one count open between marks inside a letter
- three counts open between letters, and seven between words
Pick a count slow enough to hold comfortably, around one a second to start, and keep it even. An uneven count is the fastest way to turn a message into nonsense, because a dah held for only two counts reads as a dit.
What a blinked message looks like in practice
On May 2, 1966, the US Navy pilot Jeremiah Denton was filmed answering questions in a prison in Hanoi. While he spoke aloud, he blinked a single word in morse into the camera: torture. The US National Archives record the episode as the first hard confirmation that American prisoners of war were being mistreated.
It is a good illustration of what blinking is actually for. A whole sentence is out of reach, but one word, sent slowly to anyone who knows the code, gets through where nothing else will.
Why blinking is slow
Holding an eye shut for three counts is much harder than holding a key down, and it is obvious to anyone watching. Most people settle at a pace far below the 5 words per minute at the bottom of our speed control, and stop after a word or two.
If the point is to be seen at a distance rather than to be covert, a flashlight does the same job with none of the strain, and it can run much faster. The SOS page has the counting method for a flashlight, plus a torch output that flashes an Android phone’s own light in time.
Practicing the pattern
Play the example above with the sound on and watch the lamp beside the drawing. It lights for exactly as long as each mark sounds, so it shows the pattern your eyes need to copy. When you can follow it, try it with a word of your own in the morse code translator.
Questions people ask next
Can you really send morse code by blinking?
Yes. Morse sets the timing of a signal, not the way you produce it, so anything that can be switched on and off in the right lengths will carry it.
What did the prisoner of war blink in morse code?
The word torture. Jeremiah Denton blinked it in morse during a televised interview on May 2, 1966, while answering his captors' questions out loud.
Is a blink a dit or a dah?
Either, depending on how long you hold it. A dit is one count with your eyes closed and a dah is three counts.
How fast can you blink morse code?
Far slower than a key or a flashlight, because holding an eye closed for three counts is tiring. Blinked messages are usually a single short word.
What is the easiest thing to blink in morse code?
SOS, at three short blinks, three long ones and three short ones. It runs together with no letter gaps to keep track of, and it is the one signal a stranger has a chance of recognizing.
Related answers
- Can you tap morse code?
Yes, though the standard says nothing about how.
- What does morse code sound like?
Like a single steady tone switched on and off.
- Is morse code still used today?
Yes, in the places where a plain on and off tone still beats the alternatives.
Sources
- Codes and timing follow Recommendation ITU-R M.1677-1 (10/2009), International Morse code (International Telecommunication Union, 2009).
- Scenes from hell (Eyewitness: American Originals from the National Archives) (US National Archives and Records Administration).