When I was a NOLS sea kayaking instructor we carried satellite phones for communications during an emergency. This would be the mid to late 2000's. To be polite about it, I would say this, they sucked. The audio quality wasn't great. They dropped calls all the time, they were heavy and expensive. But at the time they were the only game in town. For a lot of companies this is still the first choice for emergency communication in the backcountry.
Another company, ACR (now ACR Artex) was a long time maker of EPIRB's. (Emergency position indicating radio beacons) These were most usually found on aircraft and ships at sea. Generally a bit bigger than a coffee can, they were one time use devices that you could either trigger manually or they would trigger automatically when they hit the water. They send a signal on 406 megahertz which is a frequency specifically used for world wide search and rescue. In the 1970's a group of major nations joined to gather and split the cost of putting satellites in orbit, solely for search and rescue. They would listen for signals on 406 mhz and transfer that signal back to earth, for the coordination of a rescue. These kinds of EPIRB devices would get rescuers within about a mile of you. Then they would have to use the Mark 1 eyeball to pinpoint your location. In the Early 2000's you only had two options, an EPIRB or a Sat phone, and for the casual outdoors person they were both horrible options.
Then a little company released a new device. The SPOT. The SPOT device was inexpensive ($150) and you would have to pay for a service contract, also about $150 a year, but it was small, lightweight and powered by a pair of AA batteries. It was easy to use and a little irreverent, which sat phone companies and epirb companies certainly weren't. The box that the spot came in, said on it "by opening this box you guarantee you don't come home in one." Besides irreverence what made the SPOT different was it offered more options than what I call the "get me the hell out of here" button. It offered three options for communication. First, it offered an SOS feature that would send info via satellite to SPOT headquarters. It would show them where you are, and that you needed help and they would hand off your location and personal info to the appropriate authorities. Which is essentially what the ACR EPIRB's do, but SPOT doesn't use 406 mhz. They use a different system that is lower in power. But the Spot offered two other options. You could hit the OKAY button. Which would send an email or a text message to people on a preconfigured list. It would say something like, "this is where I am, everything is okay" and it would also send along a link to google maps showing your location. Finally there was a "help" option. This would send a message to a different preconfigured list of people, and it would say something like "Hey, I need help" and with the link to your location on google maps. But it doesn't notify the authorities. I think of this button as the "Hey, my car won't start button." In fact on the current device this has been renamed the SOV or Save our Vehicle button. SPOT was a huge step up in terms of cost and usability. But this opened the flood gates for this market space. Which bring us to where we are today.
The current crop of satellite communicators has four competitors.
The first is the only one way communicator, the SPOT Gen3. ($149) plus a user subscription that starts at $149 a year, and you have to buy a year, you can't just buy a month of service for your big trip. It works like the device described above with a few more feature options around tacking your movements. Not that different than the original but smaller, lighter and more reliable.
Next is the Garmin InReach Explorer+ 2 way satellite communicator. ($400), plus a user subscription that starts at $11.95 a month (but really gets usable at the next level which is $24.95 a month) It does everything the spot does, but when paired with a smart phone you can send custom text messages via satellite. You can receive weather reports via satellite, there are tracking features and it works as a full featured GPS for navigation. With this one you can purchase service by the month (but on the monthly "Freedom" plan, the costs are higher.
But Garmin didn't rest on its laurels, they just released the InReach Mini ($350). It shares similar plans as its big brother and does everything its big brother does but in a much smaller package. It will also pair with Garmins high end watches like the Fenix 5.
Spot didn't want to get left out in the cold, so it just released something new. The SPOT X 2 way satellite messenger. ($249.95) A bit bigger than the Spot Gen3 it has a built in keyboard that looks like an old school Blackberry. This gives you the ability to send custom text messages via satellite without having to pair it with another device like a smartphone or tablet. It too has a service plan that starts at $150.