What to do if the Internet is lost or there is no mobile connection?
Your smartphone is able to create its own network, without mobile communications and the Internet. This feature is called a dense network.
The whole point is that phones with special chat programs installed directly look for other similar phones. Either via public Wi-Fi hotspots (even without internet) or via Bluetooth which can reach up to 100 meters. It is through such a connection that a message can be transmitted to an address. In order to connect, you need to form a chain of devices.

1st program - Bridgefi. Available for Android and iOS (but iOS is very unstable). There is one significant drawback: to register on the network, you have to launch it at least once with the Internet available. You need to do this in advance, and if you don’t have time, then it will be too late and the method will not work. To establish contact, you need to be at a short distance from each other.

2nd program - Briar. Available for Android only. There is no iOS version, but it can start working completely offline, that is, if you have the apk of this application, you can distribute it and expand the grid even when there is no Internet.
The program allows you to add remote contacts using special links. When adding a link, you need to add both sides of each other. We advise you to install both for yourself and for all family members. Because it is not known which transmission method will be more successful