What is SOS and how does it work?

How it works: 15-second answer

SOS is a universal distress signal used in emergencies. It works through Morse code, which combines short (·) and long (—) signals to form letters and words. The letters SOS have this morse code sequence (· · · — — — · · ·) and are easy to recognize and transmit using sound, light, or radio waves. Modern devices can send SOS via GPS, even without a cellular network, by relaying signals through satellites. Knowing how to send it, whether by flashlight, radio, or writing could be crucial in an emergency.

What is a SOS signal?

They’re the universal distress signal used to call for help in emergencies. Whether you’re lost in the wilderness or stranded at sea, SOS can be a lifesaver. But how does it work?

But wait. Before that, we need to understand Morse codes and how they work. You'll see why we need it.

How Does Morse Code Work?

Morse code is made up of two things:

Dots (·): These are short beeps or flashes.
Dashes (—): These are longer beeps or flashes.

By mixing dots and dashes, you can make letters, numbers, and even whole words! For example:

The letter A is · —
The letter B is — · · ·
The letter C is — · — ·

Here’s how to say “HELLO” in Morse code:

H: · · · ·
E: ·
L: · — · ·
L: · — · ·
O: — — —

So, “HELLO” looks like this:
· · · · · · — · · · — · · — — —

So, you can basically write and send messages in a simple language just using dots and dashes. Now, let's get back to our topic on SOS signal.

What Does SOS Mean?

SOS doesn’t actually stand for anything, it’s not an acronym like “Save Our Souls” (though that’s a popular myth). Instead, it’s a Morse code sequence that’s simple, unmistakable, and easy to transmit in emergencies. The sequence is:

· · · — — — · · ·
(Three short signals, three long signals, three short signals)

You would have guessed why this is the sequence. In Morse code, the letters S and O are written as:

S ...
O _ _ _
S ...

Why SOS?

SOS was chosen because it’s:

Easy to remember: Three short, three long, three short.
Easy to transmit: It can be sent using sound, light, or radio waves.
Hard to confuse: The pattern is unique and unlikely to be mistaken for anything else.

How Is SOS Transmitted?

SOS can be sent using different methods, depending on the situation. Here are some common ways:

Figure 2: Drawing SOS on beach sand could save you from an uninhabited island.

Morse Code (Radio or Sound)

Use a radio, flashlight, or even a whistle to send the pattern:
· · · — — — · · ·.
For example, with a flashlight:
Short flash (·) = 1 second on
Long flash (—) = 3 seconds on
Pause between signals = 1 second off

If you're stuck on an island, then write the letter S O S on the beach sand. Also, use a flashlight to send short and long flashes as we discussed. Someone might see or hear your signal and call for help if you're in a populated area.
Digital Signals

Modern devices like smartphones can send SOS messages via text or GPS signals to emergency services.

How Does Someone Receive an SOS?

Many smartphones have an Emergency SOS feature that automatically dials emergency services and shares the GPS location.
If the SOS code is sent via VHF maritime radio (Channel 16, 156.8 MHz), nearby ships and coastal rescue stations pick it up.
When an SOS signal is sent, it’s picked up by Satellites.

No cellular connection needed: When a phone can't connect to a cellular network, it attempts to connect to a satellite to send an SOS message.
Signal transmission: The phone transmits the SOS message as a radio signal directly to the satellite.
Ground station relay: Once received by the satellite, the SOS message is relayed to a ground station, which processes it and forwards it to the appropriate emergency services.
Clear sky required: To establish a connection with a satellite, the phone needs to have a clear view of the sky.

Why Should You Care?

Knowing how to send an SOS signal could save your life or someone else’s in an emergency.

· · · — — — · · · is your lifeline when you need help the most. This is the crux of SOS and how it works!