Your comment was true, but not exactly relevant since we were talking about airtag-like devices that don’t have connectivity besides Bluetooth, saying that a device like them exists that has GPS built-in is kind of moot since they don’t have any additional ways to send that location info.

The thing you linked would fall under the walkie-talkie-like device I described.

Depending on where you are and where you hike, you may have a very different idea of what a large forest looks like than some people. Unless you’ve really traveled to go camping and hiking, or just happen to live in a very heavily forested area, what you think of as a large forest patch and what others think of may be in entirely different leagues. And just being in the woods is only part of the issue, geography has a bigger effect than all of the trees.

I’m from the Philly area, we have a pretty big wooded park, something like 2000 acres, that is entirely within the city. It’s also in a valley, so when you’re in the park there’s usually steep hills or even cliffs all around you. Cell service gets spotty in a lot of the park, even though there is probably no place in the park where you’re more than about a mile or so from major roads and cell towers and all the other stuff you expect to find in a major city, the signal just can’t get through all the dirt and rock surrounding you.

It gets even worse when you get up into the mountains, driving along a winding mountain road you can see your signal going bonkers bouncing between full bars and no bars based on what mountain is in the way of a tower at any given moment. And towers and everything else are just more spread out in general, one area I go pretty regularly to you’re often driving a good half hour or so between anything you’d really recognize as being a town, without much but woods and mountains in-between.

By contrast, I’ve also done some hiking in the NJ pine barrens, some of the sections I’ve been to absolutely dwarf that park in Philly I mentioned, and are generally more remote, but they’re mostly pretty flat, trees aren’t great for cell signals but they’re a hell of a lot better than mountains, so I can usually get pretty deep into the woods before my signal starts failing me.

I’ve also been to Quetico Provincial Park in Canada, which dwarfs pretty much any other forest I’ve personally ever been to, just an absolutely massive tract of natural area, and relatively flat at that, but it’s just so big and remote that there is really no cell service to speak of.

GPS is one-way though, your device isn’t sending anything up to the satellites, it’s just looking for where they are.

You still need a way to get a signal from the collar to your phone or computer or whatever device you’re using to track it. Things like airtags and tiles use Bluetooth to talk to nearby phones that relay it onto the Internet. If no one is close enough with a phone they’re basically useless, and if the cell service is spotty, the location can’t be updated until the phone has a signal, and depending on the area, that could be a while which means your dog could be miles from where they were when a phone last picked up the signal from their collar.

If the collar itself is hooked up to the cell network, then you don’t have to rely on someone being nearby with a phone to pick up the location, but it is still reliant on having cell service, which may not be a given if you’re out hiking in the mountains for example.

Other than that, you would have to use other satellite services, or rely on having a direct radio connection to the collar, sort of like a walkie talkie except carrying the GPS data instead of voice.

I don’t know the ins and outs of how they work, and I’m sure there’s some catch and they overall skeeve me out a bit, but I have seen a few companies that offer very limited free service, something like 25 mb/month. I don’t know how much data a gps tracker would use but that might be doable

I’m sure those companies do everything in their power to get you to pay more than nothing, automatically change your plan if you go over, deceptive emails, etc. so definitely something to be careful about. I also wouldn’t have a whole lot of confidence in those companies sticking around for very long.

And while not free, there are some pretty affordable prepaid plans and such that may be competitive or slightly cheaper than what a regular subscription might cost.

Depending on where you live, it may be possible to forego the call plan entirely, in a dense urban area with lots of open public WiFi networks, you may be able to work it entirely off of WiFi.

If you wanted to get real weird with it and jump through the loopholes to get licensed, there might also be some options using ham radio stuff like APRS, though that’s probably going to leave your dogs location exposed to any ham who happens to be playing with their radios in your area.

Now I’m not saying that any of that is necessarily a good idea or worth the hassle of setting any of that up, I’m just spitballing some ideas for what someone could potentially do if they did want to homebrew such a thing.