Radar
Introduction
Most location-sharing apps solve the wrong problem. I don’t actually want to see where my friends are on a map; I just want to know if any of them happen to be around so we can grab food. But to answer that one question, every app I’ve used wants to upload my exact coordinates to a server and keep them there.
Radar is my attempt at answering the question without the map. Open it and your friends show up on three rings: Close, Near, and Far. That’s it. No pins, no addresses, no history. If someone is close, you can ping them, they can echo back with one tap, and if enough people are in, the ping turns into a rally and a group text.
How it works
The interesting part is how the app figures out who is nearby without ever learning where anyone is. If this sounds complicated, it’s basically a set of secret handshakes.
- When you add a friend, your phones agree on a secret key that only the two of you have. The server never sees it.
- Every hour, your phone takes its rough area (a cell on a grid, not a coordinate) and scrambles it with each friend’s key. The result is a short code that means nothing to anyone else.
- Your phone uploads only those codes. The server’s entire job is to check whether your codes are equal to your friends’ codes. If they are, you were in the same area, and it knows which ring to put them on.
The server learns that two friends matched and which ring, and nothing else. It can’t turn a code back into a place, and it can’t compare codes between people who aren’t already friends. Codes are only good for a few hours, and they’re deleted the moment you unfriend someone or flip the Off Grid switch.
A few other choices follow from the same idea:
- There is no search and no contact upload. You add friends by Radar ID or by scanning their code.
- Your phone number is visible only to friends you’ve accepted.
- The “you’re near a friend’s hometown” reminder is computed on your phone, against home cities your friends already shared with you. Nothing about it goes to the server.
What’s in the app
- Radar — friends on the Close / Near / Far rings, filtered by group.
- Homebases — a map of the cities your friends call home, and a heads-up when you land in one.
- Pings — a one-line “who’s free tonight?” to some or all of your friends. Echoes update in place, and a rally turns them into a plan.
- Off Grid — one switch that hides you from everyone and deletes your codes from the server.
Try it
Radar is in beta on TestFlight for iPhone. You can join here: [TESTFLIGHT PUBLIC LINK].
If you have feedback or just want to talk about the design, email me at info@sk-apps.com.