SOS in Morse Code: Three Dots, Three Dashes, Three Dots

SOS in Morse code is ... --- ...: three dots, three dashes, three dots. Radio operators send the pattern as one unbroken signal, called a prosign, and the whole world reads it as a call for help. This page covers SOS at a glance, the letter-by-letter breakdown, the prosign form, how to write and send SOS by sound, tapping and light, what SOS stands for, the history from CQD to the Titanic, SOS compared with MAYDAY, and where SOS is still used today.

SOS in Morse Code at a Glance

SOS in Morse code has 3 letters, 9 signals and a length of 27 timing units when the letters are spaced. The table below comes straight from the translator’s engine.

A timing unit is the length of one dot. International Morse code, defined by the International Telecommunication Union (ITU) in Recommendation ITU-R M.1677-1, sets every other length from that unit: a dash lasts 3 units, the gap inside a letter lasts 1 unit, the gap between letters lasts 3 units and the gap between words lasts 7 units. SOS contains 6 dots and 3 dashes, so the signals fill 15 units. The silences fill the other 12 units: 6 units inside the letters and 6 units in the two letter gaps.

Letter-by-Letter Breakdown of SOS

SOS breaks into 3 letter patterns: S, O and S. Press the play button beside any letter to hear it alone.

S: three dots

... is three dots, spoken di-di-dit. The count is the trap: four dots is H, and two dots is I. A panicked sender who adds a fourth dot turns SOS into HOH or HOS.

O: three dashes

--- is three dashes, spoken dah-dah-dah. Each dash must last 3 units, so the O in the middle of SOS takes 11 units, more than twice the length of either S. Two dashes is M, and five dashes is the number 0.

The final S: three dots again

... closes the signal with the same three dots that open it. SOS is a palindrome in Morse code: the 9 signals read the same forwards and backwards. The symmetry makes SOS easy to remember under stress.

SOS as a Prosign: One Unbroken Signal

SOS is normally sent as a prosign, a procedural signal whose letters run together with no letter gaps. The two forms side by side:

The letter-spaced form waits 3 units after each S and after the O. The prosign form waits only 1 unit, the normal gap inside a letter, so the 9 signals sound like one long character. The prosign is 23 timing units long, 4 units shorter than the spaced form, and takes 1.38 seconds (1,380 milliseconds) at 20 words per minute (wpm).

Written text marks a prosign with a bar over the letters, or with angle brackets such as <SOS>. Paste the run-together code ...---... into the translator and the decoder returns the SOS prosign, not three separate letters. The prosigns section on the homepage lists the other procedural signals, such as the end-of-work and error signals.

A receiver reads both forms as SOS. The prosign form tells the listener that the 9 signals belong together as one distress signal, not as three letters inside a sentence.

How to Write SOS in Morse Code

To write SOS in Morse code, write three dots, a space, three dashes, a space and three dots. The written result is ... --- .... Drop the two spaces to show the prosign form.

Distress signals repeat until someone answers, so SOS usually appears three times with a slash between each repetition:

Three letter-spaced repetitions last 95 timing units. Three prosigns with word gaps last 83 units.

There are 4 common mistakes when writing SOS in Morse code:

1. Counting four dots. Four dots is H, so the message becomes HOH.
2. Writing two dashes. Two dashes is M, and SMS is not a distress signal.
3. Swapping dots and dashes. Three dashes, three dots and three dashes spells OSO.
4. Adding a slash inside SOS. A slash between letters splits SOS into three one-letter words.

How to Send SOS by Sound, Whistle and Tapping

To send SOS by sound, give three short beeps, three long beeps and three short beeps, with each long beep three times the length of a short one. Press Play on the answer card at the top of the page to hear SOS as a continuous wave (CW) radio tone.

There are 3 ways to send SOS by sound without a radio:

• Whistle three short blasts, three long blasts and three short blasts, then pause and repeat.
• Knock three light taps, three heavy knocks and three light taps on a door, wall or pipe.
• Sound a car horn or an air horn in the same short, long, short rhythm.

A tap has no length, only a start, so tapped dashes need a heavier knock or a longer press to stay readable. The tapping guide covers both methods. At a beginner pace of 5 wpm, one dot lasts 240 milliseconds (0.24 seconds), and a letter-spaced SOS takes 6.5 seconds.

How to Signal SOS with a Flashlight

To signal SOS with a flashlight, switch the light on for 1 unit for each dot and 3 units for each dash, with 1 unit of darkness between signals and 3 units between letters. A unit of half a second (500 milliseconds) reads well across open ground or water.

At a 0.5-second unit, SOS takes 13.5 seconds letter-spaced and 11.5 seconds as a prosign. Wait at least 7 units, 3.5 seconds, before each repetition. Cover and uncover the lens instead of clicking the switch, because many flashlights lag when switched. The flashlight guide covers distance, angle and phone flashlights.

What SOS Stands For

SOS stands for nothing. SOS is not an abbreviation: the signal was chosen for its sound, not for its letters. Three dots, three dashes and three dots is short, rhythmic and hard to confuse with any ordinary word.

Save Our Souls and Save Our Ship are backronyms, phrases invented to fit the letters after the signal was already in use. Neither phrase appears in the international agreement that created the signal. The letters S, O and S are the easiest way to write the pattern down.

History of SOS: From CQD to the Titanic

SOS became the international distress signal at the 1906 International Radiotelegraph Convention in Berlin, and the rule came into force on 1 July 1908. Before that date, ships used several distress calls, and operators trained by the Marconi Company used CQD.

CQD combined CQ, the general call to all stations, with D for distress. -.-. --.- -.. has 11 signals and lasts 37 timing units, 10 units more than a letter-spaced SOS. The 1906 convention chose three dots, three dashes and three dots because the pattern is shorter than CQD and hard to mistake.

Some Marconi operators kept using CQD after 1908. On 15 April 1912, the RMS Titanic sent both calls. The ship’s wireless operators first sent CQD and then switched to SOS, and the Titanic became the best-known ship to send the newer signal. The CW radio guide explains how operators still send Morse over the air today.

SOS vs MAYDAY

SOS is the distress signal for Morse code, light and sound, and MAYDAY is the distress call for voice radio. Both signals carry the same meaning: grave and imminent danger, with a request for immediate help.

MAYDAY comes from the French phrase “venez m’aider”, meaning “come help me”. Spelled out in Morse code, MAYDAY takes 65 timing units, more than twice the length of a letter-spaced SOS. Pilots and ship crews say “MAYDAY MAYDAY MAYDAY” on voice radio, and an operator with only a light or a whistle uses SOS.

Is SOS Still Used Today?

Yes, SOS is still recognised worldwide, but ships no longer rely on Morse code to send the signal. The Global Maritime Distress and Safety System (GMDSS) replaced the Morse distress watch at sea, and the system was fully implemented on 1 February 1999. GMDSS uses satellites, Digital Selective Calling and emergency position-indicating radio beacons (EPIRBs) instead of an operator listening for Morse on 500 kHz, the old distress frequency.

SOS survives in 3 places:

• Collision regulations, which still list SOS sent by any signalling method as a distress signal for ships.
• Visual and sound signalling, with a flashlight, mirror, whistle or horn, where no radio or phone is available.
• Amateur radio, where operators know the signal and relay distress traffic to the authorities.

Many phone flashlight apps and outdoor lamps also include an SOS mode that flashes the pattern automatically.

Remember SOS in Morse Code

SOS in Morse code is ... --- ...: three dots, three dashes, three dots. The letter-spaced form has 9 signals and 27 timing units, and the unbroken prosign form has 23 units. Send SOS by sound, tapping or flashlight, repeat SOS until someone answers, and call emergency services by phone or radio first whenever possible. The timing rules explain the 1:3:7 ratio behind every signal, and the help and help me pages cover the plain-English alternatives. The hello page shows the same method on a longer word.