Men rescued from Pacific island after writing SOS in sand

Remember that cloud cover is really common in a lot of places. The UK in January averages less than 2 hours per day of sunlight. You need enough satellites to image everywhere several times per day to allow for that. And even then you may have overcast weather for several days at a time.

Three dots in a triangle, three flashs in a row, etc.

Its just easy for the human mind to detect it as an unnatural pattern.

It still probably better to use SOS or help but sometimes that's not an option.

Of course they already have that. The problem isn't coverage usually, it's density of the terrain features and vegetation, and an unknown search radius in some cases.

That, and unprepared people with no way to signal a search vehicle if one comes near. That's a human problem though, not a tech problem.

If you needed help, you'd enter a text describing your situation (a default text would be used if you could only click a "HELP!" button), put the phone in a special mode that would shut everything down to conserve battery power but would send out a stronger-than-usual radio "ping" every 60 seconds or so (depending on battery). To save energy, the ping would not include the text. The repeated pings would be optimized to just shout into the ether, to get attention from the greatest distance possible.

Any receiver would recognize that it was an emergency ping and could respond with a protocol response ping that requested more info. The response would be sent at a predefined time delay and frequency that would be determined by the outgoing request ping that had been received so the phone would only have to listen to one frequency and for a brief time to save battery. The phone could rotate its outgoing pings to different frequencies but would always know when and at what frequency to listen for a response based on the outgoing ping it sent.

When it got a response from a tower, and only at that point, the phone would expend extra energy to transmit its location, the text, battery status, etc.

Based on various factors, the tower would schedule future transmissions and automate most of the data exchange to conserve the phone's power, would notify responders, and would tell the phone to notify its owner that help was being sent.

You could then put this emergency ping protocol into search and rescue aircraft and drones with mesh network abilities.

There is a lot of interest already in using both off-the-shelf and more purpose-built drone technologies in search and rescue. They currently have too many limitations: they cannot navigate complex tree canopies close enough to the ground to provide reliable visual contact with subjects; their flight time is so limited that deployment and management is a real pain for large search areas; and if they aren't fully automated then you get the same signal problems with your remote that we have with our much more powerful radios with the added benefit of extremely powerful repeaters scattered on nearby hills.

This isn't to say they can't be a resource in SAR. Alameda County brought out a brilliant array of UAV equipment after the Camp Fire and were able to survey large portions of the burned town of Paradise and then process the imagery down to almost 1 cm resolution in their IC trailer. It really was some next-gen stuff and they did it way faster than the ground pounders could survey the same area. Down in the southwest, in specific types of terrain, drones are being used to quickly survey some popular holes that hikers find their way into. And, a drone scouted an orchard and found a lost subject there about a year ago.

But you have to weigh those successes against the much larger number of cases where people with hundreds of hours of experience can still very nearly step on top of a nonresponsive subject without seeing them. Finding lost people is hard, and many of the failures to find lost people have more to do with the problems of getting bad information into IC, or searching the wrong area, or the subject being in an inaccessible area, or the lost person's remains getting quickly predated by local wildlife.

Thermal imaging likewise just does not work the way that people think it does. It doesn't work in cold environments like the Sierra in winter (western or eastern), because people are typically wearing insulated clothing and the entire area around them is a gigantic heat sink. It also doesn't work in very warm environments or in heavily vegetated environments or rocky environments with sunlight -- rocks absorb and re-radiate heat and so do plants.

I've had this conversation a few times with different technologists. What we need is a balloon that we can put up with a big ol' repeater on it. That would provide a lot more immediate benefit for search operations. But, it's not sexy, so nobody's as interested as they are in trying to fly quadcopters over impossible terrain 20 minutes at a time.

PLBs cost around $300 [1], they have five+ year batteries, and they don't require a subscription. If you need to use it, you turn it on, it grabs a GPS lock and transmits your coordinates for about a day, during which at least one satellite will see your signal and downlinks all over the planet will log your location. It may still take some time for rescue services to get to you, but finding you will no longer be the primary concern.

If $300 is still too much, you can usually rent or borrow one for the duration of your trip. Just throw one in your backpack and consider yourself lucky if you never end up needing it.

The nature of emergencies means you don't know what you're going to run into. You could be lost, you could have a broken leg, you could have been bitten by something lethal, you could be treading water 100 miles offshore. You could have provisions for a month, or you could need a medevac ASAP.

If you actually have an emergency, do you want to sit around for a week and hope that you get noticed, or do you want rescue services all over the planet to have your exact coordinates within the hour?

Ten years ago these might have been newfangled novelty gadgets, but today they really should be considered required safety equipment if you're going into an area that's remote, or where there's a real possibility of veering off course. If you're sailing a boat or flying an airplane, they're usually legally required now too. They may not be mandated for hikers or backpackers, but don't be an idiot -- you need to have one.

Rescue services don't look for lines in the sand or messages in bottles anymore. The world spent over a billion dollars to get the Cospas-Sarsat program up and running, and the expected method for signaling distress in 2020 is by satellite. You should have the equipment to make a distress call if you're going to be in a position where it may be necessary.

Don't needlessly make things harder on yourself and on rescue workers by thinking that it's manlier to flash a mirror at an airplane. That can be your backup method, but not your primary.

[1] https://www.acrartex.com/products/resqlink-400

Not to be insulting but I feel like the issue could have been solved 10 steps before the need to involve swarms of drones. If people want to go in remote areas they should carry ways to be located, there are no reasons not to carry one. It's the kind of thing that would make sense if money didn't exist, like having a police officer in front of every single house in the country to prevent burglaries.