Not the cheapest option, but this is the route I plan to take:
InReach Mini in a
Dive Case. Down side is, it's subscription based. Up side is, it's two-way communication via satellite, to dedicated rescue service and/or home. I have an InReach already, which I've used for years. The subscription package I use has an annual fee (honestly don't recall how much), and I pay month-to-month fees on top of that when I want to use it. This works out to the least expensive plan for me, because I don't get to use it regularly enough to justify full-time service (which is cheaper per month, but you're paying always...)
It's got a lot of handy features that are pretty much useless in a dive setting (except on the boat, perhaps) like two-way text messaging from your phone via bluetooth over satellite. Texts cost a bunch per message, or require a higher-grade plan, so I never utilized them. It does allow you to send unlimited preprogrammed (you set them, up to a given length) messages to preset numbers (which you can change from your online portal), so I have mine set up with "I'm leaving for my next destination now," "Checking in, everything is ok," and "I've arrived at my destination," with phone numbers for select loved ones back home. They all know what each roughly translates to in normal English. It can also automatically pin you on a map at given intervals. When I'm on a long solo motorcycle trip, it pins my location/speed to an online map every ten or fifteen minutes, so anybody who has the password can "check on me" whenever they want. If I stop outside cell reception, I can drop the generic "checking in, everything ok" message, or "I've reached my destination" if I expect to camp for the night (or several). Really really slick system, if you find yourself off the beaten path with any frequency. I've used it all over the US, parts of Canada, all over Iceland, and way out in the Pacific islands, and I've never had issues with service dropouts.
Another added bonus is that the subscription service includes search & rescue insurance, evacuation insurance, etc. And did I mention it's two-way communication, so you don't just trigger it and
hope somebody heard it and is coming for you?
Now, anybody want to buy an older, full-sized InReach so I can trade for the Mini and get the dive case?