How to send SOS with your phone flashlight, and how long each flash should be
The short answer
Send three short flashes, three long flashes, then three short flashes, with no pause between the letters, then rest for a few seconds and repeat. A long flash lasts three times a short one. A flashing light helps people who can already see you find you; it does not call anyone, so call your emergency number first if you can.
Most people know SOS as “three short, three long, three short”. Fewer know how long each flash should be, or that it is sent without the usual gaps between letters. Timing matters with light, because a signal that is too fast blurs together at a distance, and one that is too uneven looks like a faulty torch.
What SOS looks like
SOS is a Morse signal: · · · — — — · · ·. In light, a dot is a short flash and a dash is a long one.
Strictly, SOS is not three letters. It is one procedural signal, sent as a single run of nine flashes with no letter gap between the S, the O and the second S. That is what makes it recognisable, rather than three separate letters someone happened to send.
The timing
International Morse is built on one unit of time. Everything else is a multiple of it:
| Part | Length |
|---|---|
| Short flash (dot) | 1 unit |
| Long flash (dash) | 3 units |
| Dark gap between flashes | 1 unit |
| Gap between letters | 3 units |
| Gap between words | 7 units |
The standard does not fix the unit itself. A radio operator might use 60 ms or less. With light and a human watching, slower is better, because each flash needs to be clearly on and clearly off.
Kelvin uses a unit of 140 milliseconds. Worked through its own engine, that gives:
- a short flash of 140 ms and a long flash of 420 ms, each followed by 140 ms of dark;
- six short and three long flashes, so one full SOS takes 3.36 seconds;
- then a three-second rest before it repeats, so one complete cycle is about 6.4 seconds.
The rest is there for the person watching. Without it, one SOS runs into the next, and the pattern is much harder to pick out.
Sending it by hand
If you have no app, you can still send SOS with the built-in flashlight:
- Swipe down twice from the top of the screen to open Quick Settings.
- Tap the Flashlight tile three times quickly: on-off, on-off, on-off.
- Tap it three times slowly, holding each “on” for about a second.
- Three quick taps again, then pause for a few seconds and repeat.
It works, but it is hard to keep the rhythm steady, especially when you are cold, tired or frightened. The tile may also take a moment to respond. That is the case for an app that does the timing for you.
Sending it with Kelvin
In Kelvin, the dial along the bottom of the light screen has a stop marked SOS. Turn the dial to it, flip the switch, and the LED repeats the signal until you stop it. To send anything else, tap Morse, type a message, and the LED sends it letter by letter using the same timing.
Kelvin also has Safety SOS, which does more than flash. Shake the phone three hard times while the app is open, or tap the red SOS button: the LED loops SOS, the screen pulses red, a loud siren plays even on silent, and your SMS app opens with a help message to up to three people you chose, with a map link to where you are if you switched location on. You get three seconds to cancel a shake you did not mean, and the message goes only when you press Send. It is set up once, in Settings, then Safety SOS.
Two practical notes. The strobe and SOS modes flash rapidly, and fast flashing can trigger seizures in people with photosensitive epilepsy, so do not point it at anyone up close. And a flashing LED uses battery steadily. Kelvin’s auto-off timer, set in Settings, can turn the light off after 1, 5, 15 or 30 minutes so it cannot flatten the phone without you noticing. Set it to Off if you need the signal to run for longer.
What a flashing phone can and cannot do
A phone torch is a small light. It can help a search party or a passing car that is already looking your way. It will not be seen over a hill or through trees, and it does not tell anyone where you are.
So the order matters:
- Call first. If you have any signal, call your local emergency number: 112 works across India and Europe, and 911 in the US and Canada. Many phones can make an emergency call with no SIM.
- Share your location with someone you trust, if you can. In Kelvin, one SOS opens a message with a map link to up to three contacts at once.
- Then signal. Use SOS when you can see lights, hear people, or know someone is searching.
- Save the battery between signals. A dead phone cannot call or flash.
For a softer light while you wait, Kelvin’s Screen mode turns the display into a lamp. And if you are deciding which torch app to keep for moments like this, read why a flashlight app does not need camera permission.
- Flashlight
- Safety
