[DoingIsLearning]

For large gatherings you can have Bluetooth connected mesh networks. There are apps that already implement this out of the box like Bridgefy or Briar.

You can have a network of consumer radio walkie talkies with privacy codes, each node spread with a range of about 20km, depending on the weather and terrain. But this is would need dedicated hardware which I assume is not easily sourced in the current restricted environment.

Edit: Maybe if you setup a network of walkie talkies on rooftops you could probably maximize the node spread if are able to keep line of sight across each node.

[barbegal]

Are there any documents describing the actual user experiences of using Bridgefy or Briar in a real life scenario. They seem like cool tools using interesting technology but I am not convinced that they work well in practice and it is difficult to find much information about where they have been used successfully.

[iansowinski]

Not a document but Hong Kong protesters use it https://www.bbc.com/news/technology-49565587

[barbegal]

This article only states that the app had been downloaded more during the protests. Reviews in the app store suggest it doesn't work reliably.

[DoingIsLearning]

For full-disclosure I have no first hand experience with Bridgefy or Briar, I suggested the former because it seemed like an alternative to _Firechat_ (which apparently is no longer available).

Having said that, irrespective of the Application layer, all BT based mesh networks are inherently fragile.

There are large performance variations accross BT chipsets (old/new and different manufacturers) and externals like BT firmware, OS variations, battery level, RF blocking/reflecting structures nearby, Law enforcement jammers, the number of nodes available (the more nodes in a narrow area the more fault tolerant it is), all of these factors affect the performance of such a network.

The point is, OP is asking for help to scope out what are the options. None of them are great, but the best we can do is to bring forward the known options and hope that those struggling in this situation are able to implement whatever they need to remain safe.