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Show HN: Red Grid Link – peer-to-peer team tracking over Bluetooth, no servers (github.com)

54 points by redgridtactical ↗ HN
I go on a lot of backcountry trips where I barely get cell service. If my group splits, nobody knows knows where anyone is until you regroup at camp or at your destination. You can buy Garmin radios or try to set up an ATAK, but ATAK is Android-only and assumes you have a TAK Server running somewhere to make use of all of the functionality. Cool tools themselves, but expensive to set up correctly. I just wanted two iPhones to share their location directly over Bluetooth when cell coverage was lacking.

Red Grid Link does that. Start a session, and anyone nearby running the app shows up on your offline map. When they walk out of range their marker stays as a "ghost" that slowly fades.

The hard part was making sync reliable over BLE. The connections drop all the time. Someone turns a corner, walks behind a vehicle, whatever. I built a CRDT sync layer (LWW Register + G-Counter) so there's never merge conflicts. Each update is just under 200 bytes (from what I have tested so far). When a user/teammate disappears the app does exponential backoff from 2 to 30 seconds before giving up and marking them as a ghost.

Everything is encrypted (AES-256-GCM, ECDH P-256 key exchange per peer pair). Sessions can require a PIN or QR code to join. It also offers offline topo maps with MGRS grid coordinates, same system as in my other app, Red Grid MGRS.

The app is free, and I'm looking for some honest feedback from other real-world users. Let me know if you have any questions!

14 comments

[ 5.2 ms ] story [ 47.3 ms ] thread
shminge
Very cool idea. What's the range of BLE connectivity? I can't imagine it gets far
idiotsecant
Isnt the range of Bluetooth pretty much the range of a loud yell?
RankingMember
Cool idea, but doesn't Meshtastic already do this but with better range because it uses radio instead of BT?
seriousmice
Super cool idea! This would be amazing for Airsoft games
[dead] _jbos
[flagged]
deknos
I cannot wait until it's in an appstore for android and that it will work with android/iphone together. And i seriously hope you do not abandon it. That being said, i have questions:

1. When i have a higher version, but others have a lowerpaid version, can i still connect to more members, or am i constrained by the lowestpaying customer in the network? 2. Do you have reproducible builds? 3. airdrop sadly only works with iphones, how will this be done with android? 4. would it be a possibility, that after some time you made decent money, you consider a even higher paid stage, where i can fully build the best /most feature version myself? just in case you ever leave the project? 5. https://github.com/RedGridMGRS/RedGridMGRS is a 404 for me? 6. Would it be possible you also use openstreetmap or better to say integrate map loading from there? 7. Would you consider adding something like https://www.fixphrase.com / what3words-alternative into the app, so coordinates could be uses with phrases?

pabs3
Have you considered adding WiFi when someone goes out of BLE range?