SOS Signal
· · · — — — · · ·
Three SHORT — Three LONG — Three SHORT
Pause 3 seconds. Repeat.
Morse Code: Critical Characters
| Letter | Code | | Letter | Code | |---|---|---|---|---| | A | · — | | N | — · | | B | — · · · | | O | — — — | | C | — · — · | | R | · — · | | D | — · · | | S | · · · | | E | · | | T | — | | H | · · · · | | U | · · — | | I | · · | | V | · · · — | | K | — · — | | W | · — — | | L | · — · · | | Y | — · — — | | M | — — | | Z | — — · · |
Numbers
| 1 | · — — — — | 6 | — · · · · | |---|---|---|---| | 2 | · · — — — | 7 | — — · · · | | 3 | · · · — — | 8 | — — — · · | | 4 | · · · · — | 9 | — — — — · | | 5 | · · · · · | 0 | — — — — — |
Timing: Short (·) = 1 unit. Long (—) = 3 units. Gap between elements = 1 unit. Gap between letters = 3 units.
SOS: The Only Code You Must Know
SOS is not an abbreviation. When it was adopted as the international distress signal in 1908, it was chosen specifically because the pattern — three shorts, three longs, three shorts — is simple to transmit, simple to recognize, and distinct from any common word.
In radio: Transmitted on 500 kHz (historical) and increasingly on 2182 kHz and digital emergency frequencies.
In light: Three quick flashes, three slow flashes, three quick flashes. Any light source works. Signal toward aircraft engines, toward distant observers, toward the sky if you don't have a specific target.
In sound: Three short blasts, three long blasts, three short blasts on a whistle, horn, or by striking metal.
The pattern is universal. Any rescue professional worldwide will recognize it.
Flashlight Signaling Technique
Day: A flashlight beam is nearly invisible in daylight. During the day, use a signal mirror instead. Reserve the flashlight for night.
Night: A flashlight or headlamp in strobe mode is visible 1-3 miles from the air and can be seen much farther if the observer is adapted to darkness and you're in a clear, open location.
Technique:
- Face the aircraft (estimate direction from engine sound)
- Point the light toward the aircraft
- Signal SOS: three short flashes, three long flashes, three short flashes
- Pause three to five seconds
- Repeat
Strobe mode: Many modern headlamps and survival lights have a dedicated strobe mode. An automatic strobe is more effective than manually flashing SOS because it produces a consistent, rapid flash that's highly visible. Use strobe continuously when an aircraft is in the area, and manually signal SOS when an aircraft might be watching.
Beyond SOS: Simple Morse Messages
Knowing a handful of additional characters lets you send simple messages with a flashlight, radio transmitter, or any signaling device to a person who knows Morse.
Useful short messages:
- HELP: · · · · / · / · — · · / · — · ·
- INJURED: · · / — · / — — — / · ± — — · — / · — · · / — — — / — · · ·
- WATER: · — — / · — / — / · / ·
- Your grid coordinates or location as numbers
Amateur radio operators, military personnel, and many pilots and mariners know Morse. In a scenario where you can establish any kind of communication with a trained operator — on any frequency, by light, or by any other method — even simple Morse can carry critical information.
Equipment
A standard flashlight or headlamp works fine. For a dedicated emergency signaling device:
- Adventure Medical Kits SOL Emergency Strobe: Waterproof, 3+ mile visibility, 8+ hour battery, $20
- ACR ResQFlare: Combined signal light and flare, USCG approved, $25
- Any headlamp in strobe mode: Already in most kits, free
Don't buy special equipment just for light signaling unless you do extended wilderness travel. The light you already carry is sufficient if you know the technique.
What matters is that the light is accessible — on your person, not in the bottom of a pack — when you need it.
Sources
Frequently Asked Questions
How do you do SOS in Morse code?
SOS is three short flashes, three long flashes, three short flashes: · · · — — — · · · . In practice: three quick clicks, three slow clicks, three quick clicks. Pause, repeat. There are no spaces between the letters in SOS when used as a distress signal — it's transmitted as a continuous block. SOS was chosen as the international distress signal partly because it's easy to send and easy to recognize.
Can aircraft see a flashlight from the air?
A quality flashlight (200+ lumens) can be seen from the air at distances of 1-3 miles at night. A strobe light (many survival lights have a strobe mode) can be seen farther. The signal must be directed toward the aircraft — sweeping the beam toward the sound of the engine is more effective than random flashing. Modern survival strobes visible to 3+ miles are available for $15-25 and run for 8+ hours.
Is it worth learning full Morse code?
For most preppers, knowing SOS plus a few critical characters (letters A through Z are not required) is sufficient for emergency signaling. Full Morse proficiency requires months of practice to reach useful speeds. However, knowing enough Morse to spell your name, location, and HELP via simple messages is achievable in a day of study and would be useful in a long-duration crisis where you're communicating with radio operators.