If you are lost, stranded or injured and your phone has no signal, a flashlight may be your best way to call for help. SOS is the one Morse code pattern that almost everyone recognises, it works in any language, and sending it needs no equipment beyond something that can be switched on and off. This guide covers exactly how to do it — the rhythm, the timing, the aiming — and what to do if you don’t have a flashlight at all. For the background on the signal itself, see SOS in Morse Code.

The pattern

SOS in Morse code is:

· · · − − − · · · — three short, three long, three short.

Spoken aloud: di-di-dit, dah-dah-dah, di-di-dit. That’s it. There is no “save our souls” acronym to remember; the pattern was chosen in 1906 precisely because it is simple and impossible to mistake for anything else. Sent as one unbroken group, followed by a pause, then repeated.

How to flash it

  1. Three short flashes. Turn the light on and off three times quickly. Each flash should last about half a second to a second.
  2. Three long flashes. Turn the light on for roughly three times as long — two to three seconds — three times, with short gaps between.
  3. Three short flashes again.
  4. Pause for three to five seconds — long enough that a watcher can tell the group has ended.
  5. Repeat. Keep going steadily, for as long as you can, ideally from the same spot. Rescuers need time to notice, look again, and confirm.

A common mistake is to rush. A slow, even rhythm with clearly different short and long flashes is far easier to recognise than a fast, ragged one. If you are nervous, count — “one” for a short, “one-two-three” for a long — or say the di-di-dit, dah-dah-dah out loud as you do it.

If you have a phone with you, our SOS page has a Flash button that turns the whole screen into a blinking SOS at the correct rhythm, so you don’t have to count at all. Set the brightness to maximum and hold the screen towards where help might come from. Most modern phones also have an “Emergency SOS” mode in the settings that flashes the camera LED — worth learning before you need it.

How to make and break the flash

Switching a flashlight on and off repeatedly is slow and hard on the switch. Better options:

  • Leave the light on and cover the lens with your palm, a hat or a piece of cloth, uncovering it for each flash. This gives crisper, faster signals.
  • Use a headlamp or bike light with a strobe only if it has a Morse/SOS mode — a plain fast strobe is not SOS, though it still attracts attention.
  • Use the camera flashlight on your phone through a dedicated SOS app or the Flash button mentioned above.

Where to aim

Light carries surprisingly far at night — a small LED torch can be visible for several miles in clear conditions — but only in the direction you point it.

  • Aim at where rescuers are likely to be: a road, a lit town, the coastline, a passing vessel, a helicopter or aircraft. Aircraft: lead them slightly and keep the signal going; a pilot sees you for only a few seconds.
  • Get high and open. A ridge, a clearing or a beach beats a valley floor or dense trees.
  • Sweep slowly across the horizon between SOS groups if you have no idea where help is, then repeat the signal in each direction.
  • At night, switch off between groups so the signal stands out against a constant light source.

Signalling in daylight

A flashlight is almost useless in sunshine. Use a signal mirror instead — or any reflective surface: a phone screen, a watch face, a polished can lid, a CD. Hold the mirror near your eye, extend your other hand and form a V with two fingers around the target, then angle the mirror until the reflected spot of light falls on your fingers; now the flash is on the target. Tilt it on and off in the SOS rhythm. Signal mirrors have been seen by aircraft more than 10 miles away.

No light at all? Use sound or movement

The SOS pattern works with anything:

  • Whistle: three short blasts, three long, three short. Far less tiring than shouting and carries further. (Note the common simpler convention, especially in mountain rescue, of six blasts per minute, then a minute’s pause — both will be understood as distress.)
  • Banging on metal or a pipe, car horn, or tapping on a wall if you are trapped — the classic use of Morse in collapsed buildings.
  • Ground signals for aircraft: if you can, also lay out a large SOS on the ground with rocks, branches, or trampled snow — letters at least 3 m (10 ft) tall, in a colour that contrasts with the background.

Recognising a reply

If someone has seen you, they may respond with a single long flash, by flashing SOS back, or with three flashes of any kind. Keep signalling until you are sure they are coming to you, then conserve your battery: one group every few minutes is enough to guide them in.

Before you need it

  • Practise the rhythm once, now, so it is automatic: tap it out on our tap decoder and watch it read “SOS”.
  • Pack a small flashlight and spare battery, a whistle and a signal mirror in any hiking or boating kit. They weigh almost nothing.
  • Learn where the emergency/SOS feature is on your phone.
  • If you are curious to go beyond SOS, learning the rest of the code takes only a few weeks — start with How to Learn Morse Code.

FAQ

How long should each flash be? Short flashes about one second; long flashes about three seconds; a similar one-second gap between flashes and three to five seconds between groups. The ratio matters more than the exact timing.

Do I flash SOS continuously? Send the group, pause, repeat — continuously for as long as you can, ideally from one spot. Once you have a reply, slow down to save battery.

What if I only have my phone? Use the screen (with the Flash button on our SOS page) or the camera LED via an SOS/flashlight app or the phone’s built-in emergency mode, and keep the brightness at maximum.

Is three flashes of anything an SOS? Three of anything — flashes, whistle blasts, fires — is a widely recognised distress signal even without the full SOS pattern. The full pattern is simply more unmistakable.