I own two:

One is simply a locator beacon--push the button, it sends out a SOS and a homing signal. Mine was about $250, needs refurbishment/replacement every 5 years. (Technically you could just replace the batteries yourself but it's safety gear, you don't cheap out!) I bought this when I was sometimes hiking not as part of a group, but still in areas where there are others passing by. This is basically a miniaturized version of the emergency locator transmitters on aircraft--it gives up something in the way of duration and while it's built tough it's not meant to survive an aircraft going in, but mine is about 4 oz. It could be smaller but I chose the version that's built to float. Note that these are only intended for emergency use.

Second is a Garmin inReach--I bought it last year because of the pandemic I was hiking away from others (at one point I'm pretty sure I was the first person on that route in months, although my objective could be reached another way. The majority of my cool-season hikes I have not seen anybody--there's no way I would go out there alone without some way to call for help!) IIRC ~$450 and it has a monthly service charge. The basic plan gives you 10 texts/month, going over is 50 cents/text. I do not recall the non-contract rate. I'm on the mid-tier contract level, $25/mo (comes out a bit over $26) which gives me 40 texts/month (which I've never needed) and unlimited breadcrumbs at 10 minute intervals (which is why I pay for that plan--even if for some reason I can't call for help the breadcrumbs will get search and rescue very close.) Note that while you are not charged for SOS messages you still have to have a service plan for them to get through at all. You can text any phone, anyone you text can reply (within a certain window whose size I do not know) and you can give people a password to text you through the website. I have no idea how it works for texts between two devices. I also have three presets that must be set up on the computer. They can be used without charge.

Note that the target audience for such devices is people like me--those that head off into the wilderness where we have no cell service and few people around. Since I have the inReach I would take it along as backup comm on a road trip but I certainly wouldn't get it for that purpose. Note that it probably won't work in a car and messages are slow as it only periodically polls the satellite (normal mode is 10 minute intervals.)

Some competitors to the Garmin units have come along in recent years and I believe there have been more entrants recently. At the time I bought mine I considered the Garmin units to be built tougher than the others I had seen and there's not much difference in the service.