I just looked up this APP and I agree with Mudcrone that it is a valuable tool for getting aid or advice for yourself AND reporting crime or bad behavior that you witness. It is FREE, well organized, easy to use the language of your choice.
It transmits your location to the police when you open the app and choose "Call" or "Chat". You can have that location feature "on" all the time or only when you open the APP. You can also link the APP with three other travelers/friends/family also on the Camino and see their location and vice versa.
You populate the fields you want with the info you want to share and you can add in the notes area special things the police should know such as medications or medical conditions or other contacts etc... In these times I think we are reluctant to share more info than the minimum on any APP but when we find ourselves in an emergency, where it might be hard to think straight or we are injured and it is very difficult to talk/type and provide the basic info to the authorities, having done all of that before the emergency could be very convenient if not life saving. It loaded fast on my phone and has very good instructions and FAQ's. When my trip is over, I will delete the APP. Then I will download it just before arriving on the next trip to Spain.
Calling 112 (911 in the USA) is reserved for extreme, life threatening situations. I and probably you too are reluctant to use it. This APP gives you the chance to communicate with law enforcement for any and all levels of assistance. I'll probably never use it but if I find myself in that unenviable situation where I need it, I will be so glad I have it at the ready. (I just hope I can remember that I have the APP - I think I will move it to my opening-first screen on my phone just before I leave for Spain to help remind me every day that I have that special tool on board).
Does the phone's cellular service need to be on?
I don't know the answer for sure to this question and I am not good with technology but I assume if you choose to alert authorities via a voice phone call or a text (they use the word "chat" in the APP) then yes you need cellular service. I believe in some situations with a very weak or no apparent cell signal, texting can work when a voice call will not. If you are able to access WIFI, then maybe you would not need cell service.
There are Satellite Phones and less expensive Satellite Messaging devices made by Garmin/Delorme, SPOT and probably others that use satellites not only for location to send out a S.O.S./Rescue Me Now, but some can also handle short 2-way texting to communicate important information. Maybe this technology will be built into our phones in the future but right now this technology requires additional hardware that takes up additional physical space. These satellite phones start at about $600 to purchase and then the plan you buy for service is very expensive. Calls to a land line are about $1/minute, calls to and from other satellite phones can be $15/minute. Satellite Messaging devices also require a service plan that at a minimum will be about $250/yr and enable you a small allocation of text messaging. The plans go up in price quickly with more features and more text message allocation. Going over your plan's limits incurs more charges. If on a budget re: $$ and weight, these devices are low priority, especially on the busier Camino routes where cell phone coverage is almost everywhere and the next hiker, town or house that can render some help is almost always within a few kilometers.
The typical buyer for these satellite Phones and Messaging Devices are hikers in very remote areas where there is no chance of finding a cell signal for prolonged periods of time...wilderness or out at sea. Those who use them in populated areas do so for family peace of mind as much as the ability to send out an emergency "rescue me" signal. The family peace of mind includes knowing their is S.O.S. capability but mostly it's the feature that allows them to track your progress on map on their home computer, seeing where you stop each night, how long you rest, what kind of pace you are keeping and the short text msg at the end of of the day saying "I'm ok". This can offer great comfort to a spouse who stays home while their loved on is on the Camino. Plus, they can confirm their Spouse (or the satellite messaging device) is actually slogging through the hot Meseta and not gallivanting in Monaco with a lover.