SOS is a distress signal. It was adopted as the international distress prosign by the 1906 International Radio Telegraphic Convention, and it remains the internationally recognized distress pattern today.
The exact rhythm of SOS is three short signals (dots), three long ones (dashes), then three short ones again. In Morse code, this sequence reads “... --- ...” – or three dots; three dashes; three dots. This sequence is known as the “SOS” prosign because the three letters S, O, and S each can be expressed with their corresponding sequences:
S = …
O = ——–
S = …
Putting these together yields “… ——– …”, which you can use as a mnemonic for how to send an SOS signal.
When sending SOS as a continuous prosign, you should not add any spaces between elements. A prosign is a series of joined together signals. Instead, when transmitting SOS as a distress call, simply repeat the entire nine-element sequence over and over again.
Timing
Each element within the SOS distress call takes up a certain number of International Morse units, which represent either the dot or dash duration. While you could choose to send SOS at a faster pace, the important thing is that your speed is steady, and that the ratio between your long and short pulses remains constant. As such, the timing of SOS is:
Dot = 1 unit
Dash = 3 units
Gap between joined elements = 1 unit
Long about three times the short
Because you’re sending SOS in its entirety as one single, continuous signal, it’s important to ensure that your short and long pulses are clearly contrasted. Whether you’re tapping on a wall, blowing into a whistle or horn, blinking your eyes, or flashing a light, all SOS signals must be composed of three short flashes followed by three long flashes followed by three short flashes again. If you use a flashlight or lantern to signal, you might find yourself repeating the sequence several times.
Using Other Methods
There are also other ways to transmit SOS. Tapping on walls, pipes, or floors uses similar techniques: three quick taps, three slow taps, and then three more quick taps. Each of these actions sends out an instant impact tap, while sustained pressing, scraping, or using a buzzer or vibration may be used to produce the longer pulses.
While the 1906 convention set a standard for SOS transmission, there’s no requirement to wait any specific length of time between repetitions. Some sources suggest waiting just a couple seconds or counting a few beats before beginning again, but if you want to avoid confusion, consider simply repeating the entire SOS group once more. That said, a brief interval isn’t enough to distinguish one repetition from another, so make the pause clear after you have completed the entire sequence.
SOS Meaning and Recognition
In many ways, SOS is quite simple. After all, the idea behind it is pretty straightforward: get people’s attention, and let them know that they need assistance. However, it’s often easy to conflate SOS with some of the other backronyms we have today. For instance, “Save Our Souls” became a popular backronym after SOS had already been established, with no official phrase behind the original signal. Others include “Save Our Ship,” “Stop All Signals,” “Send Only Signal,” “Security Operation Started,” and many others. Regardless of which backronym becomes popular, SOS remains a distinctive Morse sequence that doesn’t require decoding.
That’s not always true, though. For example,HELP is encoded letter by letter and transmitted individually, rather than as a continuous prosign. It carries an English-language message, like HELP ME, rather than serving as a standardized prosign. Since the English language is involved, someone attempting to decode a message will need to understand what the sender is saying.
But SOS is different. There’s no need to speak English, or to know anything about the receiver, in order to recognize an SOS. If you’re receiving an SOS signal, then you know you need to respond. That pattern is what makes the continuous distress prosign especially recognizable even to an unknown recipient.
It’s also important to remember that although the maritime radio use of SOS ended in 1999 when the Global Maritime Distress and Safety System replaced it, SOS is still a recognized distress pattern. And, after all, it’s still useful for anyone who has access to a simple media, like light or sound, that can be used to signal someone else.
If you’re ever lost, stranded, or injured and need assistance, SOS is still the easiest way to signal that you need help.