How to know when a friend is nearby without tracking anyone
Quick answer
You can know when a friend is nearby without sharing live location: keep a private list of where they live and let your phone check distance locally, then ping you when you get close.
There are two ways to catch a friend when you are close. The first is live location sharing, where an app streams everyone's position and drains the battery. The second keeps a private list of where friends live and checks distance quietly on your phone. With that second method, nothing leaves your device. You only get a tap on the shoulder when you actually end up near one of those saved spots.
In one sentence
Parages pings you when you pass near a friend. It tracks nobody.