Like pitchforks and placards before them, smartphones should be a powerful protest tool. But when cell towers get overloaded with traffic or governments decide to restrict Internet access, they’re as good as useless. Both have happened in the weeks since Sept. 27, when protests broke out in Hong Kong over Beijing’s decision to vet candidates for upcoming elections. And yet phones have played an integral part of the continuing demonstrations.
The reason? FireChat, a smartphone app that allows users to communicate even when they can’t get online or send texts. FireChat directly connects users to other nearby users who are within 250 ft. (76 m) via Bluetooth or local wi-fi. More people in range can then join the chat, extending the network. Protesters have been using the app to coordinate and support one another–all without an Internet connection.
In the two days after protests broke out, some 200,000 people in Hong Kong downloaded the app, says Micha Benoliel, CEO of Open Garden, the company that makes FireChat. It skyrocketed to the top of the region’s app-store charts for both Apple iPhones and Google Android devices. Open Garden, a San Francisco–based startup, was founded in 2011 and has raised about $2 million since. The company, which also offers apps that make it easier to find open wi-fi networks, didn’t create FireChat specifically for protesters. The app is also used at crowded public events such as music festivals and football games.
But FireChat’s popularity among protesters isn’t a complete surprise. The app was used by Taiwanese protesters in March, making it the latest in a long line of technology that has helped fuel political dissent. Iran’s 2009 Green Revolution was dubbed the Twitter Revolution thanks to protesters’ organizing via the microblogging site. And 2011’s Occupy Wall Street movement had a hashtag even before it was a real-world street protest.
Still, FireChat isn’t perfect. The chat rooms are open, making them easy to join–and monitor. The company is currently working on a version with more privacy measures. “If this application can help in this way, it’s very aligned with the mission of the company,” Benoliel says. “We are very supportive of what’s happening here in Hong Kong.”
This appears in the October 20, 2014 issue of TIME.