SOS in Morse Code

Why SOS is sent as one unbroken signal

SOS is not really three letters. It is a procedural signal (a prosign): nine marks sent as one block, ...---..., with no letter gaps between the S, the O and the second S. Radio manuals write it with a line over the top to show this.

The translator treats what you type as letters, so it shows ... --- ... with a space after each letter. Both forms mean SOS, and both are understood. To hear the unbroken version, type ...---... into the Morse code box: the Text box shows SOS, and Play sends the nine marks without letter gaps. The Morse code decoder reads ...---... as SOS too.

At the default 20 WPM, the spaced version lasts about 1.6 seconds and the unbroken one about 1.4 seconds. When you send by hand, that small difference doesn't matter. What matters is the 3, 3, 3 rhythm, then a clear pause before you repeat it.

How to send SOS by light, whistle, mirror or tapping

The rule is the same for every signal: a dash lasts about three times as long as a dot, and the pause between rounds is longer than any pause inside SOS. Go slower than you think. Someone far away needs to tell each short from each long.

• Flashlight or lamp: three short flashes, three long, three short, then dark for a few seconds. The Beginner speed preset (5 WPM) in Sound settings makes each dot about a quarter of a second, a good pace to copy.
• Whistle: three short blasts, three long, three short. Many hikers and rescuers know a plain three blasts as a call for help, so if you are tired, three blasts repeated also works.
• Mirror: tilt a mirror or anything shiny to flash sunlight toward a plane, a boat or a hillside. Short and long flashes are harder to control here, so keep the pattern slow.
• Tapping or knocking: on a pipe, a wall or a hull, knock three quick, three slow and spaced out, three quick. A knock can't be held, so slow knocks stand in for dashes.
• On the ground: stamp S O S into snow or lay it out with rocks or logs, as large as you can. It reads the same upside down, so it works from any direction in the air.

Loop, Flash and the flashlight

Loop replays SOS after a word gap until you press Stop. Mute turns the sound off while the lamp, the tape and the flash carry on, which helps when you want a silent light signal. Both choices are kept in this browser.

Flash shows a warning first, because flashing light can trigger seizures in people with photosensitive epilepsy. Then a small light in the middle of a dark screen turns white for each dot and dash. Full screen makes the whole screen the light, which is easier to see from far away; it plays at 7 WPM or slower so it flashes no more than 3 times a second. Press Esc to close it. With Loop on, it keeps flashing SOS.

Use flashlight switches the phone's camera light in time with the code. It works in Chrome on Android only; iPhones can't control the flashlight from a web page, so use the screen flash there.

In a real emergency, call first

If you can make a call, call your local emergency number (911 in the US) before anything else. A call gets help moving faster than any signal. Morse code SOS is a fallback for when you can't call: no service, a rescuer you can see but not reach, or a moment when you can't speak.

The "Emergency SOS" feature on iPhones and many Android phones is not Morse code. It calls the emergency number for you, and can send your location to your emergency contacts. It doesn't beep or flash ... --- ...

Where SOS came from

Germany used ...---... as a distress call in its radio rules from April 1905. The first International Radiotelegraph Convention, signed in Berlin on November 3, 1906, made it the world standard from July 1, 1908.

Before that, operators of the Marconi company sent CQD (-.-. --.- -..), starting in 1904. CQ was the general call to all stations, and D was added for distress. In poor reception CQD could be taken for a plain CQ, while SOS was hard to mistake. British operators kept using CQD for years, and in 1912 the Titanic's operators sent both CQD and SOS.

At sea, SOS by Morse code was replaced in 1999 by the Global Maritime Distress and Safety System, which uses satellites and digital calls. The signal itself stayed: people everywhere still know three short, three long, three short as a call for help.

SOS doesn't stand for Save Our Souls

SOS was chosen for its sound, not for words. When it was agreed in 1906, it wasn't an abbreviation. "Save Our Souls" and "Save Our Ship" were attached to it later, as memory aids. Spelled out, Save our souls is ... .- ...- . / --- ..- .-. / ... --- ..- .-.. ... in Morse code, far longer than the nine marks of SOS.

For other short messages, see Morse code words. To ask for help in plain words, there is help in Morse code.