Show HN: Red Grid Link – peer-to-peer team tracking over Bluetooth, no servers

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!

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RankingMember an hour ago | parent | next [-]

Cool idea, but doesn't Meshtastic already do this but with better range because it uses radio instead of BT?

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redgridtactical an hour ago | parent [-]

Meshtastic is great if you're willing to carry extra hardware. Everyone in your group needs a LoRa radio (which can range from $30-50 each), and you need to pair them, flash the firmware, configure channels, etc. For a SAR team or preppers who already own the gear, it's definitely a solid choice.

Red Grid Link was more so for those already carrying their phones and those that don't want to buy anything else. The trade-off is range for convenience. BLE gets you maybe ~50-100m in the open, ~20-60m in densely woooded areas. That's enough to keep tabs on a hunting party spread across a hillside or a hiking group. Absolutely not a replacement for a radio relay across a valley.

Different tools for different problems. If I need a 2km mesh range I'd set up Meshtastic too.

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RankingMember 36 minutes ago | parent [-]

Good points. I like the ghost marker functionality, helps with the shorter-range of BT.

	▲	redgridtactical 7 minutes ago \| parent [-]
		Thanks, yeah the ghost markers ended up being one of those features that came out of necessity. Once I accepted that the BLE range was never going to be amazing, the question became what happens when someone drops off? Felt wrong to just remove them from the map.

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seriousmice an hour ago | parent | prev | next [-]

Super cool idea! This would be amazing for Airsoft games

	▲	redgridtactical an hour ago \| parent [-]
		Definitely was one of the use cases I designed around!

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shminge an hour ago | parent | prev | next [-]

Very cool idea. What's the range of BLE connectivity? I can't imagine it gets far

	▲	redgridtactical an hour ago \| parent [-]
		It's not long range by any stretch. The use case is more "my group split up on a trail and I want to know which fork they took" vs "track someone across a mountain." The ghost marker system helps here too. If someone walks out of range, their last known position and direction stays on your map, so you at least know where they're heading and how long ago they traveled that direction.

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idiotsecant an hour ago | parent | prev [-]

Isnt the range of Bluetooth pretty much the range of a loud yell?

	▲	redgridtactical 5 minutes ago \| parent [-]
		Haha fair point. In open terrain you get maybe 50-100m which I agree, not far. In practice it's more useful than it sounds though. You don't need miles of range when the point is "where did my buddy go 5 minutes ago." And if they walk out of range their last position and heading stick on your map as a ghost marker so you're not totally blind or left guessing.