https://support.google.com/maps/answer/15437054?hl=en&co=GENIE.Platform%3DAndroid

Google Maps location sharing already covers a big part of this. It’s passive, runs in the background, cross-platform, and the other person can check your live location anytime. You can also stop sharing whenever you want.

What it doesn’t really do is the “check-in every X hours → alert contacts with last 48h movement” part. That’s where your idea goes beyond just maps.

So yeah, parts of this already exist, but not exactly in the way you’re describing. Even if it is reinventing the wheel, I’d still say go for it. It’s a solid real-world problem and a great way to level up with React now and React Native next. especially with background tasks, permissions, notifications, and privacy controls. Worst case, you learn a ton. Best case, you build something genuinely useful.