Send Morse code with a flashlight by using short flashes for dots and longer flashes for dashes. The timing is the same as radio Morse: a dash lasts three times as long as a dot, gaps between letters equal three dot-lengths, and gaps between words equal seven dot-lengths, per ITU-R M.1677-1. Any device that produces a short or long signal works: flashlight, signal lamp, mirror, buzzer, whistle, or horn.
The Basic Timing Rules (Same for All Media)
| Element | Duration |
|---|---|
| Dot (short flash or beep) | 1 unit |
| Dash (long flash or beep) | 3 units |
| Pause within a letter | 1 unit (off/silent) |
| Pause between letters | 3 units (off/silent) |
| Pause between words | 7 units (off/silent) |
Choose a unit length you can produce consistently. For casual light signaling, 1 second per unit is comfortable:
- Dot: 1-second flash
- Dash: 3-second flash
- Letter gap: 3-second darkness
- Word gap: 7-second darkness
At 1 second per unit, the word “HELP” takes about 55 seconds to send. Practiced operators work much faster.
Light Signal Methods
Flashlight or headlamp: Point at the receiver and flash short or long. This works up to about 1–2 miles (1.5–3 km) at night with a standard flashlight in clear conditions. Cover the lens with your hand or a dark cloth between flashes rather than switching the light on and off (which wears out the switch faster and is slower).
Signal mirror: A mirror reflects sunlight in a beam visible over 10 miles (16 km) in good conditions. Tilt the mirror to flash the beam at the target: quick tilt = dot, hold on target = dash. Military survival kits often include a signal mirror for this reason.
Phone screen: Turn your phone’s flashlight on and off, or put the screen at maximum brightness and tilt it toward the receiver. The phone’s camera light is easier to modulate than the screen.
Signal lamp (Aldis lamp): Professional maritime and military signal lamps produce a concentrated beam for ship-to-ship and ship-to-shore communication. They use a trigger or shutter mechanism to produce precise dots and dashes.
Sound Signal Methods
Buzzer or horn: Short sound = dot, long = dash. The ratios are the same as light. Any buzzer, car horn, boat horn, train whistle, or compressed air horn works.
Whistle: Short toot = dot, long toot = dash. A whistle is a standard item in survival kits, and Morse SOS (· · · — — — · · ·) is recognizable from a whistle to anyone who knows it.
Tapping: Short tap = dot, long tap or held knock = dash. Tap on a pipe, wall, or hull. Trapped survivors in collapsed structures have been located this way, because vibrations travel through solid materials where voice cannot.
Sending SOS with a Flashlight: Step by Step
SOS is the international distress prosign, adopted internationally on 1 July 1908. Sent as a single unbroken sequence:
- Three short flashes (S): flash — pause — flash — pause — flash
- No extra gap (stay in the same prosign)
- Three long flashes (O): long flash — pause — long flash — pause — long flash
- No extra gap
- Three short flashes (S): flash — pause — flash — pause — flash
- Longer pause, then repeat from step 1
Pauses between flashes within the same letter are equal to one dot-length. Because SOS is sent as a prosign (not three separate letters), the pause between the S-group and O-group is also just one dot-length.
Sending “HELP” with a Flashlight
| Letter | Code | Flash pattern |
|---|---|---|
| H | …. | short short short short |
| E | . | short |
| L | .-.. | short long short short |
| P | .–. | short long long short |
Between H and E: 3-unit pause. Between E and L: 3-unit pause. Between L and P: 3-unit pause.
Night vs. Day Signals
At night, a flashlight is highly visible. In daylight, a signal mirror works much better because it produces a bright reflected sunbeam. Flash the mirror by tilting it so the reflected spot crosses the target: a quick tilt is a dot, holding the reflection on target is a dash.
A standard survival technique is to aim a signal mirror at any aircraft or vessel even if you do not know Morse — the flashing reflection alone attracts attention.
Practical Tips for Light Morse
- Keep your rhythm consistent. Irregular timing confuses the receiver.
- Send slowly enough that the receiver can decode each character. You can increase speed as you practice together.
- Use a natural break point (end of word) to let the receiver catch up.
- If the receiver does not respond after three SOS repetitions, repeat every few minutes while conserving your battery.
Use the Morse code translator to convert a message to dots and dashes before signaling. For the full timing rules, see Morse code timing explained. For a history of SOS and how it became the universal distress call, see SOS meaning and history.