There are few things quite as frustrating as dealing with a loss of power. In many cases, that wouldn't cut off communication entirely, as most of us have cell service that would allow us to keep in contact. But what about in the case of a full city power outage? It's happened, and it makes the loss of power at your own home seem like a cakewalk.
In extreme cases, it could be governments that are causing disruption, with a notable case being Hong Kong last year, during the Umbrella Revolution. As this was going on, people were unable to make use of their mobile service to keep in contact with each other. Fortunately, there was a solution: FireChat.
FireChat works by bouncing messages off of other FireChat users, until they reach their destination. It doesn't rely on cellular towers at all, but does require the support of mobile users who are willing to install the app. In the event of a power outage or some governmental overstep, people will still be able to keep on contact with others, provided the overall support is good. It should be noted though that FireChat's angle isn't only power outages. Those who simply want to keep their messages off the grid could make good use of the service.
According to FireChat's developers, it requires just 5% of mobile users in a given city to consider it "blanketed". However, when you consider that the vast majority of people don't install apps based on what "could" happen, 1/20 people does seem ambitious.
The company's "OM" service isn't the fastest, but that's to be expected when cell towers are bypassed. It's said that a message could take upwards of 10 minutes to be delivered, with the entirety of the latency being the sum of all the devices the message has to pass through.
It's not fast, but it does seem cutting-edge, even though the technology to pull it off doesn't seem that complicated. I admit I am tempted to install the app, as last summer, my city did suffer nearly a complete power outage. Fortunately, cell service was still working, but I could have easily been in a situation where it wasn't. Sometimes it's better to be safe than sorry.