SOS in Morse Code and How to Send It: Calling for Help with a Light, Sound, or Whistle
SOS, “• • • − − − • • •”, is the best-known Morse signal in the world. Yet few people can send it correctly with light or sound when it counts. This article covers the code and rhythm of SOS, how to send it with a flashlight or phone light, whistle and tapping signals, mountain distress signals, the origin of SOS and how it differs from CQD and Mayday, and what to prioritize when you really need help.
SOS is three short, three long, three short, sent in sequence
SOS in Morse code is three dots, three dashes, three dots: “• • • − − − • • •”. As sound, it’s “dit dit dit, dah dah dah, dit dit dit”; as light, it’s three short flashes, three long flashes, three short flashes.
Strictly speaking, SOS isn’t the three letters S, O, and S, but a single distress signal defined as nine elements sent continuously with no letter breaks (•••−−−•••). Even so, sending it with small gaps between letters still comes across fine as SOS. What matters is that short and long are clearly distinct, and that you repeat it many times.
| Element | Length ratio | Rough timing when sending by hand |
|---|---|---|
| Dot (•) | 1 | About 0.5 s |
| Dash (−) | 3 | About 1.5 s |
| Gap within a letter | 1 | About 0.5 s |
| Gap between letters (S and O) | 3 | About 1.5 s |
| Gap before repeating SOS | 7 or more | About 3.5 s or more |
Remembering that a dash is three times a dot is enough. There’s no need to send fast as in radio; a slow, big rhythm is more reliable, so people far away or unfamiliar with Morse can tell it apart.
Sending with a flashlight or phone light
Light signals at night can be seen from far away. To send SOS with a flashlight or phone light, follow these steps.
- 1
Point it toward whoever you want to reach
Aim the light in the direction of the people you want to see it, such as a ship, helicopter, or building across the water. Holding it steady in a chosen direction carries further than waving it around.
- 2
Flash by covering it with your hand, not with the switch
Phone light switches respond slowly and don’t suit fine flashing. Keep the light on and cover and uncover it with your palm or clothing to make accurate shorts and longs.
- 3
Three short, three long, three short
Three short flashes of about 0.5 seconds, three long flashes of about 1.5 seconds, then three short flashes again. When finished, stay dark for a few seconds and repeat the same signal.
- 4
Keep going while saving battery
It can take time to be noticed. Send intensively when you sense people or ships nearby, and keep the light off otherwise to make the battery last.
In the daytime, reflecting sunlight with a mirror or phone screen reaches further than a light. When keeping watch for signals in the dark for long periods, also allow for the time your eyes need to adjust. See How Eyes Adapt to the Dark for how that works.
Signaling with a whistle or by tapping
When trapped in a building or somewhere with poor visibility, sound reaches further than light. Shouting continuously in a disaster drains your strength and risks inhaling dust, so the basics are an emergency whistle or tapping a wall, pillar, or pipe with something hard.
- Whistle: three short, three long, three short. Blow dots and dashes with the length of your breath.
- Tapping: it’s hard to vary the length of a tap, so simply repeating “three taps” with pauses in between signals that someone is there.
- Pipes and steel frames carry sound well, so if one is nearby, make it your tapping spot.
- Signaling when you hear the voices or sounds of rescuers makes it easier for them to find you.
The mountain distress signal is six times a minute
There’s also the “International Mountain Distress Signal” (the Alpine Distress Signal), which spread from Europe’s mountain regions. Whatever the method (whistle, light, or waving your arms), send it with the following rhythm.
| Signal | Rhythm |
|---|---|
| Calling for help | Signal 6 times in 1 minute (once every 10 seconds), then rest 1 minute. Repeat |
| Reply from whoever notices | Signal 3 times in 1 minute (once every 20 seconds), then rest 1 minute |
The advantage is that even people who don’t know Morse SOS can notice it as a regularly repeated signal. When preparing for a hike, along with a light and whistle, also review how much water and trail food you’re carrying. How Much Water You Need for Hiking also explains how to think about what to pack.
The origin of SOS, and how it differs from CQD and Mayday
SOS was adopted as a distress signal at the International Radiotelegraph Convention in Berlin in 1906 and came into use from 1908. Before that, CQD, used by Marconi company stations, was widely used as a distress signal, and in the 1912 sinking of the Titanic both CQD and SOS were sent.
- SOS is sometimes said to stand for “Save Our Souls” or “Save Our Ship”, but those explanations were added later. It was actually chosen because its sequence of dots and dashes is simple, easy to remember, and hard to mishear.
- Mayday is the distress signal used on radiotelephones (by voice). It’s said to come from the French “m’aider” (“help me”), and it does by voice the same job as Morse SOS.
- For ships on international voyages, distress communication moved entirely to GMDSS (the Global Maritime Distress and Safety System), which uses satellites and other means, in 1999, and Morse distress communication ended its role. Even so, SOS remains widely known as a signal that can also be sent by light or sound.
When you really need help, call first
Morse SOS is a last resort for situations where phones can’t connect or your voice can’t reach anyone. If a phone works, call first.
- In Japan, call 119 for fire and ambulance, 110 for police, and 118 for incidents at sea. Elsewhere, call your local emergency number.
- Smartphones have an “Emergency SOS” feature that places an emergency call through actions such as pressing the power button. How it works varies by model and settings, so check on your own phone in advance.
Practice the rhythm of SOS with sound and light
Enter “SOS” in the Morse Code Translator & Trainer to play “• • • − − − • • •” as sound and as flashes of an on-screen light. Slowing it to about 5 WPM gives a slow rhythm close to sending by hand. Try using it with family or kids to practice copying it with a whistle or light.
For the codes of other letters and numbers, see the Morse Code Alphabet and Numbers Chart, and for the codes of Japanese kana, see the Japanese Wabun Morse Chart.
FAQ
- What is SOS in Morse code?
- “• • • − − − • • •” (dit dit dit, dah dah dah, dit dit dit). As light, it’s three short, three long, three short flashes, properly sent continuously with no letter breaks.
- How do I send SOS with a flashlight?
- Keep the light on and flash it by covering and uncovering it with your hand for accuracy. A short flash is about 0.5 seconds and a long flash three times that, about 1.5 seconds. After each signal, stay dark for a few seconds and repeat.
- What does SOS stand for?
- It doesn’t stand for anything. “Save Our Souls” and the like are explanations added later. It was actually chosen as a distress signal because its sequence is simple, easy to remember, and hard to mishear.
- What’s the signal for being lost in the mountains?
- With the International Mountain Distress Signal, use a whistle or light to signal 6 times in 1 minute (every 10 seconds), rest 1 minute, and repeat. Whoever notices replies with 3 signals per minute. If your phone connects, call emergency services first (110 or 119 in Japan).
- What’s the difference between Mayday and SOS?
- Both signal distress, but SOS is Morse code (by telegraph, light, or sound), while Mayday is spoken over radiotelephone.
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