Have you considered the Delorme In Reach?
I am not affiliated with this company other than being a customer of their product and service only.
I just got back from thru-hiking Death Valley with a friend 10 days ago and used the SOS feature due to my hiking partner not showing up at a meeting point on the route. With this experience I found the two way satellite communication to became an invaluable tool that helped myself and Death Valley SAR in the decisions and planning of the events. What transpired was, after my hiking partner didn’t show and became an hour late to the meeting point, I began to back track to find him. After two hours of actively looking and it now being 2:00 PM, I decided to activate the SOS feature on the unit. My decision to do this at that time was based on knowing Tom is now three hours late, it takes time to get a SAR team called up, briefed on the situation, travel time to the location and I was hopeful they could start the search before nightfall.
With the two way communication I was able to give them a detailed brief of the situation including;
Where he was last seen, name age & physical description, hiking experience level, gear and food carried, possible medical problems and meds, phone numbers to family members, GPS and triangulated physical description of my location, GPS location of the food/water cache and destination of the days hike, and my experience level and understanding of the situation (I’m a Wilderness EMT, Vol.Wilderness Ranger for Los Padres NF and retired Fire Fighter with 34 years service). Being that I had the tracking feature active during this hike, the SAR team was given my exact route hiked for the day by Delorme. I am very happy with how the communication between myself-Delorme and SAR was shared, with the SAR guys telling me they were very impressed with all of it.
The end result was that my partner pulled a bone head move, deviated from the hike plan and hiked around me at a lower elevation, then continued to the cache site, got a cell signal and called me, wondering where I was. I brought him up to speed on the afternoons events, the SAR was concluded and we finished hiking thru Death Valley three days later. For me, I hike solo 99% of the time, I think it will be 100% from here on out.