SOS in Morse Code
Three short, three long, three short. Play it below, or let your screen flash it.
...---...
Three short, three long, three short - sent as one continuous signal.
At this speed the screen flashes more than three times per second. If you are sensitive to flashing light, set the speed to 7 WPM or lower.
SOS is a genuine distress signal. Sending it over the air, by light or by sound when there is no emergency ties up rescue services and is a criminal offence in most countries. Use it here to learn and to listen.
SOS in Morse code is ...---... - three dots, three dashes, three dots, sent as one continuous signal without the usual gaps between letters. It was agreed at the Berlin radio conference in 1906 and came into force on 1 July 1908. The letters do not stand for anything; the sequence was chosen because its rhythm is impossible to mistake for anything else.
Why the SOS signal is not three separate letters
Written out as letters, S O S would be ... --- ... with a three-unit gap after each one. The distress signal has no such gaps: it runs straight through as nine elements in a row. That is what makes it recognisable even through heavy interference, and it is why the correct written form places a bar over the letters in older publications.
The practical effect matters. A listener who hears the gaps hears three ordinary letters that could be part of any message. A listener who hears the unbroken run knows immediately that someone is in trouble.
What SOS actually stands for: nothing
Save Our Souls, Save Our Ship, Send Out Succour - all of these were invented after the fact. They are mnemonics, not origins. The 1906 conference was looking for a signal that was short, unmistakable in rhythm and easy to send by an operator under pressure. Nine elements in a simple three-three-three pattern fit that better than anything else on the table.
Before SOS there was CQD, introduced by the Marconi company in 1904: CQ was the general call to all stations, and D stood for distress. It was never an international standard, only a company practice, and it was easily confused with an ordinary CQ. When the Titanic went down in April 1912 her operator sent both - CQD first, then SOS as well.
The phrases came later, and there is a word for that: a backronym, an expansion invented after the abbreviation already exists. SOS is one of the most widely repeated examples, which is why almost everyone knows a meaning for it and almost nobody knows the right one.
SOS and Mayday: the same emergency, two channels
They are not alternatives. Each belongs to a different way of transmitting, and the second exists because the first does not survive being spoken.
- SOS is the radiotelegraph signal - wireless telegraphy, sent in international Morse code as dots and dashes. It works because a rhythm carries through noise that would swallow a voice.
- Mayday is the radiotelephone call, for speech. Frederick Stanley Mockford, in charge of radio at Croydon Airport, proposed it in the early 1920s from the French m'aider, and it went into service on cross-Channel flights in February 1923. The International Radiotelegraph Convention in Washington adopted it in 1927 alongside SOS.
The reason for a second word is worth knowing, because it says something about Morse code as well: spelling out S-O-S by voice is unreliable, since the letter S is hard to tell apart on a telephone circuit. What is unmistakable as rhythm is ambiguous as sound. Mayday is spoken three times at the start of a call for the same reason SOS runs together without gaps - so that nobody can mistake it for part of an ordinary message.
A third term belongs beside them: pan-pan, also spoken three times, for urgency without immediate danger to life. There is no Morse equivalent in everyday use.
Is SOS still in use?
As a radio procedure, no. The Global Maritime Distress and Safety System replaced Morse distress calls, and the last commercial Morse watches were stood down in 1999. Ships now send digital alerts that carry their identity and position automatically, and the ITU Radio Regulations no longer require anyone to listen for the signal that wireless telegraphy was built around.
As a signal between people, very much yes. SOS survives wherever there is no radio: a torch flashed at a search aircraft, a whistle, a mirror, marks stamped into snow, a pattern tapped on a pipe. It needs no equipment and no shared language, which is exactly why it has outlived the technology it was invented for.
In the mountains, SOS is the wrong signal. The international alpine distress signal is six signals per minute, then a pause of one minute, repeated - not the Morse pattern. The answer is three signals per minute. Rescuers in the Alps are trained on that rhythm, so use it there rather than SOS.
How to send SOS by light or by sound
- By light. With a flashlight, a phone torch or a mirror: three quick flashes, three long ones, three quick ones, then a pause of several seconds before repeating. Keep the long flashes clearly about three times the length of the short ones - the rhythm carries the message, not the brightness. Cover and uncover the lens with your hand rather than clicking the switch; it is faster, quieter and easier to keep even.
- By sound. Same pattern with a whistle or by knocking. Sound travels through rubble and around corners where light cannot.
- Repeat with pauses. One burst is easy to miss or dismiss as a reflection. A repeating pattern with a steady gap reads as deliberate.
- Slow is fine. There is no minimum speed. A clear signal at eight words per minute beats a rushed one nobody can parse.
Frequently asked questions
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What is SOS in Morse code?
SOS is
...---...: three short signals, three long ones, three short ones, sent as one continuous run with no gaps between the letters. -
Does SOS mean Save Our Souls?
No. That phrase and others like Save Our Ship were attached to the signal long after it was adopted. SOS was picked in 1906 purely for its rhythm, which is short, symmetrical and hard to confuse with anything else.
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When was SOS adopted?
It was agreed at the International Radiotelegraph Convention in Berlin in 1906 and took effect on 1 July 1908. Germany had already used the same sequence in its national regulations from 1905.
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What did ships use before SOS?
CQD, introduced by the Marconi company in 1904. CQ called all stations and D marked it as distress. It was a company convention rather than an international rule, and it sounded too much like a routine call.
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How many dots and dashes is SOS?
Nine signals: three dots, three dashes, three dots. In timing units the distress signal is 23 units long, against 27 for the three separate letters S O S. Those four units are the two letter gaps that are left out, and leaving them out is the whole difference between a message and a distress call.
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What is the difference between SOS and Mayday?
The channel. SOS is the Morse code signal for radiotelegraphy; Mayday is the spoken call for radiotelephony, adopted in 1927 because the letter S is hard to distinguish by voice. Both mean the same thing: immediate danger to life. Pan-pan, also spoken three times, is the lesser step for urgency without that danger.
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How do you write SOS when it is repeated?
Each repetition is a signal of its own, so it is
...---..., a pause of several seconds, then...---...again. Running them together into one endless string removes the pause that tells a listener where the pattern begins, and the pattern is the whole point. -
Is it illegal to send SOS when there is no emergency?
Yes, in most countries. A false distress call diverts rescue services from real emergencies and is treated as a criminal offence. Listening to the signal here or learning to send it is fine; broadcasting it is not.
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Should I use SOS if I am lost in the mountains?
No. Use the alpine distress signal: six signals within one minute, a full minute of silence, then repeat. Mountain rescuers are trained to recognize that rhythm, and the reply you should watch for is three signals per minute.