SOS in Morse code

How SOS is written and timed

SOS is nine signals: three short, three long, three short. Each long signal lasts three times as long as a short one, and the pauses inside the pattern are as long as a short signal. Sent as one character, the whole pattern takes 23 units. Sent as three separate letters, it would take 27, because the gap between letters is three units instead of one.

At 6 words per minute a unit lasts 200 ms, so one SOS takes about 4.6 seconds; at 12 words per minute it takes about 2.3. Then comes a pause, and the signal starts again. The player above sends it as one continuous character, the way it is written: .

How to signal SOS with a flashlight

1. Give three short flashes, each about as long as it takes to say “dit”.
2. Give three long flashes, each about three times as long as a short one.
3. Give three short flashes again.
4. Pause for a few seconds, then repeat the whole signal.

The same rhythm works with a whistle, a car horn or by knocking: what matters is that long is clearly longer than short. Point the light at the people you want to reach and keep it aimed at them while you signal.

If you can reach the emergency services by phone, call them first. A light or sound signal is for when you cannot.

On a screen, very bright flashes can be a risk for people with photosensitive epilepsy. Web accessibility rules ask that content flash no more than three times in any one second (WCAG 2.2, criterion 2.3.1), which is why the Flash button on this site keeps its signal slow.

Where SOS came from

The signal was set by the International Radiotelegraph Convention, signed in Berlin on 3 November 1906, and came into force on 1 July 1908. Its service regulations say: “Ships in distress shall use the following signal: [] repeated at brief intervals” (ITU History Portal, Berlin 1906).

The regulations define the pattern of dots and dashes, not a word. The letters do not stand for “Save Our Souls”: the International Maritime Organization calls that a popular myth and says the signal was chosen because it is easy to remember and transmit (IMO, 1999).

Is SOS still used at sea?

Not as the main distress system. The Global Maritime Distress and Safety System became fully operational on 1 February 1999, and on that date Morse code was phased out for ships covered by the SOLAS convention, which includes passenger ships and cargo ships of 300 gross tonnage and more on international voyages (IMO, 1999). The pattern is still worth knowing by sound and by light for the moments when a phone is not an option.

Practice it

Type SOS or any other word into the Morse code translator to hear it, watch it flash or copy the code. The Morse code alphabet has every letter, and How to learn Morse code by ear explains how to recognize them without counting.