I have had an InReach for 5 years. Two-way texting, as someone mentioned above. I send a preset message to my family each evening when I make camp; this message says all is well and gives them the coordinates of my camp.
Other available services: emergency aid, map tracking, more frequent messages, custom weather report, etc.
The InReach is small and portable. It holds its charge very well. It can tether to my iPad or iPhone via the Earthmate app for downloading maps or for using the iPad keyboard to type messages.
InReach uses two satellite systems. It will send out a message from any place where you can see the sky. It doesn't usually work inside the RV; holding it out the window sometimes does the trick. Outside, under trees, not so good; moving out of shade to a more open area solves that.
One service offered by Spot which is not yet available for InReach is the Save Our Vehicles program. InReach brings aid for people.
https://explore.garmin.com/en-US/inreach/ Owner's manuals are available on the Garmin site; read them so you know what you are getting.
Please note that you have to be conscious to push the button that sends for help. It might be a good idea to show your travel partners how to use the device.