Communication is critical during any emergency, but whenever a natural disaster strikes, it's often unreliable. Congested cell phone networks and damaged infrastructure can make it difficult for rescue workers to disseminate information, and for loved ones to get in touch with one another. A new app aims to change that.

The makers of FireChat, a smartphone app for offline messaging, have today announced a new app that allows rescue agencies to send alerts even when cellular networks and internet connections are unavailable. Called FireChat Alerts, the app uses peer-to-peer networking technology, known as mesh networking, to push alerts to smartphone users within a given time frame and geographic area. Those within affected areas will receive the alerts through the FireChat app, which will then automatically store and forward them to other FireChat users who are within range (typically about 200 feet in urban areas). Christophe Daligault, chief marketing officer at Open Garden, says the app was designed as a simple way for organizations to provide information "to the people who need it most."

"What's interesting about this approach is that it doesn't require any new hardware or even any difficult configuration," Daligault said in a phone interview this week. "It's just software, which means that it can be easily deployed and can scale infinitely. There's no need for hardware because the hardware's already there."

FireChat first gained popularity at festivals like Burning Man, though it has also seen spikes in activity during protests, elections, and natural disasters, when cellular networks may be blocked, congested, or damaged. The app creates mesh networks by linking phones via Bluetooth and peer-to-peer Wi-Fi, with each device functioning as a node in the network. The mesh network strengthens as the number of users increases, making it ideal for densely populated cities like Manila. Since launching in 2014, FireChat has been downloaded more than 7 million times.

Open Garden, the San Francisco-based startup that created FireChat, says its new app can be used by government organizations, rescue workers, and media organizations to send both text and visual information during emergencies. The company developed FireChat Alerts as part of a pilot program in the Philippines —€” which sees about 20 typhoons a year —€” and in collaboration with the UN Office for the Coordination of Humanitarian Affairs (UNOCHA).

Rescue workers could use FireChat Alerts to send messages from within an affected area with zero internet connectivity, though those on the periphery could also receive information over the internet and automatically transmit over the mesh network to disconnected users. Daligault says that in a typical urban area with 5 percent penetration, it would take about 20 minutes for a message to reach every FireChat user; in densely populated areas like Manila, it would only take "a couple of minutes."

Other organizations have used mesh networking to connect people during protests, when governments have shut down internet access, or to provide connectivity to underserved neighborhoods. Marco Di Felice, a professor of computer science at the University of Bologna, says mesh networking holds a lot of promise for connecting people "in situations where cellular infrastructure is down," though he says there are some drawbacks. The technology wouldn't be able to reach people in rural areas when disasters bring down networks, and people would have to be using the same app to communicate.

"You need to have a lot of people on the app, otherwise you will try to send a message and no one will receive it," says Di Felice, who has studied the potential for mesh networks in emergency communications. "And this is not trivial."

Open Garden has released an SDK that would allow government agencies to incorporate the same functionality in their own apps, and Daligault acknowledges the importance of having enough users on the same platform.

"You want to make sure that everyone has [the app] before disasters happen," he says. "In the case of hurricanes and typhoons you get early warnings, in the case of earthquakes, not so much... When it's too late, it's too late."