80,000 phones, one mesh

The cell towers at a festival do not fail dramatically. They degrade. At 10am a message takes two seconds. By noon it takes forty. By the time the headliner walks on, the little spinner is the only thing anyone's phone is doing, and the group chat that was supposed to hold ten friends together has quietly stopped being a group chat.

We spent three days on that field with 40 phones running Nobars and a notebook. The short version: the mesh got denser exactly when the network got worse, because everyone who gave up on signal was standing still and holding a radio.

3.4

Average hops per delivered message

1.8s

Median time to first delivery

96%

Messages delivered inside a minute

Crowds are good radio

Bluetooth hates walls and loves people-shaped bags of salt water rather less, but a crowd is not a wall. It is a few thousand slow-moving relays, most of them at chest height, most of them pointed at a stage. A message heading from the food trucks to the north gate did not travel in a straight line. It rode along the queue.

That exchange happened, in some form, forty or fifty times over the weekend. The interesting part was never the first message. It was the second: the moment someone realises the thing in their pocket is still a radio, and that the failure they had accepted was a failure of one particular network, not of physics.

What broke

• Names. Half the field picked the same three nicknames, and Nearby turned into a list of six people called “sam”. Safety numbers fixed it; nobody read them. We're fixing the first-run screen instead.
• Battery anxiety. Nobars used about 4% over a nine-hour day. People still turned it off at 20% because every other app had taught them to. We now say the number in the app.
• Rejoining. Walk out of range for twenty minutes and come back, and a pending message could take two minutes to find you. That's a store-and-forward tuning problem, and it's on the roadmap.

What we're taking back

Density is a feature, not a hazard. The next release spends less time scanning when there are dozens of peers in range and more time relaying, which cut battery use again in our own follow-up test in a packed subway car. And the first-run screen is getting the one instruction that mattered on the field: stand next to your friend, scan once, and you are done for good.