Sometimes survival options come down to "SOS" – an international distress signal. In the mid-1800s, Morse Code was used for the first electronic communication device: the telegraph. The letters "SOS" don't stand for anything in particular, such as "Save Our Ship" or "Save Our Souls." In Morse Code, the letters "SOS" simply create an unmistakable sound pattern: three short - three long - three short - pause - repeat: dot-dot-dot, dash-dash-dash, dot-dot-dot (· · · – – – · · ·), and they're easy to remember in an emergency.
The term "SOS" now refers to all distress signals - with or without Morse Code - and vary depending upon where you are.
Search/rescue aircraft look for large SOS letters spelled out on the ground (the bigger, the better - of course). You can use rocks (or whatever) to show a sharp color contrast on plain surfaces - such as using dark rocks on a pale surface. And vice-versa: using pale rocks on a dark surface. OR... it's easier to make three large X marks in the shape of a triangle, such as:
If you use a car's horn [or a personal security alarm (noisemaker or screamer) or a simple whistle], do three short blasts, three long blasts, three short blasts - pause - repeat. If you use taps or bangs (such as through a wall), do three quick taps, three slow taps, three quick taps - pause - repeat.
• Sailors use whistle blasts or light flashes to send Morse Code SOS distress signals (three quickly - three slowly - three quickly - pause - repeat).
• Airplane pilots and other radio callers use a “Mayday! Mayday! Mayday!” distress signal. It’s more vocally distinctive for a spoken radio message. It’s adopted from the French word “m’aider” (‘help me’) and is to be spoken three times in a row (“Mayday! Mayday! Mayday!”) then pause and repeat.
• Campers can send three puffs of smoke or lay out 3 markers in a large triangle to signal a search plane. After dark, you can send Morse Code SOS with a flashlight. Or you can use 3 campfires in a triangle (as in the X marks in the shape of a triangle above).
• A hiker (in a highly visible location) should slowly and repeatedly raise and lower outstretched arms (on each side) – with hands describing a large circle. And yell "Mayday!" or "Help!" repeatedly.
• Hunters fire three gunshots.
• Mountain climbers use six long whistle blasts or light flashes, repeated at one-minute intervals.
• “Pan-pan” is adopted from the French word “panne” (a ‘breakdown’) and is used vocally for a non-life-threatening predicament – though it’s not widely known in most countries.
• If you're choking on food and need someone to perform the Heimlich maneuver on you, summon help from bystanders by grasping your throat. A rescuer will stand behind you and bear-hug you with their fist and support hand just above your navel - then give your belly a sharp squeeze to push forcefully into your diaphragm and force air out of your lungs – thereby blowing out the food lodged in your throat. It may have to be repeated multiple times to succeed. [If you're alone, perform the Heimlich maneuver on yourself by placing your fist just above your navel and fall onto a tabletop (or something similar) so your fist will force air out of your lungs (as above). It may have to be repeated multiple times to succeed.]
• Drivers with a CB radio call for help on either channel 9 or 19. Since you can use your voice over the radio rather than blasts or taps, you can say "Mayday! Mayday! Mayday!" - pause - repeat.
• Call the police, fire department, or ambulance, of course. See 911 Calls.
• If you're attacked in a populated area (where somebody helpful can hear you) yell, "Help! Police!" (see Kitty Genovese - Article Bank).
For greater distances (as described above), she can slowly raise and lower her outstretched arms (on each side) repeatedly – her hands describing a large circle. (Though that's an internationally known distress signal, it's not as well known as the other distress signals described above.)
See visuals of the SOS Signal - Silent Hand Code
• Carry a Personal Security Alarm (screamer or noisemaker) at all times.