I use paralino on grapheneOS. I have been using it for a year or so. You can have groups like family or friends and create locations so you can get alerts when someone leaves or arrives. There is a subscription fee but it isn’t a lot and only one person needs to buy it. Everything is end to end encrypted and only exists between the devices. There isn’t a central server storing your data. I would rather self host something but at the time I wasn’t prepared to do it and now it just works for me.