There seems to be a lot of "public service announcement" posts circulating on social media at the moment stating something like -
PSA – If you are ever lost while hiking, get stranded with a broken down car, etc and you notice your cell phone is either low on juice or has no signal, here is a tip that very well may save your life.
Change the voicemail on your phone to a message that gives your approximate location, the time, the date, your situation (lost, out of gas, car broken down, injured, etc) and any special instructions such as you are staying with the car, you are walking toward a town, etc…. The best part of this is that even if your cell phone dies or stops working, voicemail still works, so anyone calling your phone looking for you will hear the message and know where to find you or where to send help.
In the UK (and it applies in other countries too), just don't do this!
If your phone is low on battery, this will use lots of precious 'juice' or has no signal this advice won't work - you need signal to record a new voicemail.
Every mobile phone user should consider registering their phone here - https://www.emergencysms.net/ and know how to use the service (what to send, and to wait for a reply).
The benefit for outdoor folk is that an emergency text uses very little 'juice' to go, and will find the smallest amount of signal to go, and significantly in windy conditions there is no distortion of a voice call.
REMEMBER if you have a little amount of battery power left, the police and Mountain Rescue can use SARLOC to locate you to within 10m-50m - read more about it here.
Please think about sharing things like the purported PSA, fact check these things and do what so many of our emergency services have been asking us to do for ages!