SOS in Morse Code

What does SOS mean?

SOS is the international Morse code distress signal: ... --- .... Despite what you may have heard, it does not stand for “Save Our Souls” or “Save Our Ship” — those are backronyms invented later. The sequence was chosen purely because it is simple, unmistakable and easy to send under stress: three short signals, three long, three short. Officially it is a single prosign written with a bar over the letters (SOS), meaning the nine signals are sent as one continuous group with no gaps between the letters.

Because it is symmetrical and has such a distinctive rhythm, SOS can be recognised even by people who know no other Morse code, and it works with any medium — sound, radio, a flashlight, a mirror, a whistle, or tapping on a pipe. That universality is why it has outlived the telegraph era and still appears on emergency beacons, phones and survival guides today.

How to signal SOS

1. Three short

   Send three quick signals — three short flashes of a torch, three short whistle blasts, three short taps. Each one lasts about one unit.

2. Three long

   Follow immediately with three long signals, each about three times as long as a short one. Keep the gaps between signals short and even.

3. Three short, then pause and repeat

   Finish with three more short signals, wait a few seconds, and repeat. Keep going at a steady pace until you get a response.

How to signal SOS with a flashlight

Point the light towards where help is likely to come from — a road, the shore, an aircraft — and cover and uncover the lens or use the on/off switch to make the signals. Three short flashes, three long, three short, then a pause of a few seconds before repeating. Aim for a consistent rhythm rather than speed; a slow, clear SOS is far easier to recognise than a fast, ragged one. If you have a phone, the Flash button above turns the screen into a blinking SOS so you don't have to count.

There is a complete walkthrough, including what to do at night, in fog, and with a mirror in daylight, in our guide How to Signal SOS with a Flashlight.

A short history of SOS

Before SOS, the Marconi company used CQD (“CQ” — all stations — plus “D” for distress). Germany adopted ... --- ... for its radio regulations in 1905, and the 1906 International Radiotelegraph Convention in Berlin made it the worldwide standard, effective 1 July 1908. The first documented rescue using SOS came in 1909, when the liner Arapahoe lost her propeller off North Carolina.

The signal's fame was sealed in April 1912 when the Titanic's wireless operators sent both CQD and SOS as the ship went down. SOS remained the official maritime distress call until 1999, when the satellite-based Global Maritime Distress and Safety System (GMDSS) replaced Morse for commercial shipping — but it is still universally recognised, and still taught, for exactly the situations where no system is left but a light and a steady hand. More in The History of Morse Code.