Protesters in Hong Kong are staying off the grid and making themselves harder for the authorities to trace by using a Bluetooth-based messaging app that does not require the internet to run.
Hundreds of thousands of demonstrators are coming under ever-increasing scrutiny from police in the territory, after months of protests against a now-suspended extradition bill that would have seen people sent to mainland China for trial in Communist Party-controlled courts.
In a bid to avoid potential detection by authorities, and bypass a potential clampdown on internet access, many have turned to an app developed by a startup tech firm in San Francisco.
Bridgefy allows users to communicate with each other and the public using what is known as a mesh network, which establishes direct connections between devices rather than via the internet.
Messages can bounce between different smartphones that have the app installed to reach their destination, allowing them to travel across the whole city if needed despite a limited 100m range from handset to handset.
Users can also communicate with people who are not on their contacts list, with the app capable of broadcasting private chats to anyone within range who has it installed.
It means protesters can avoid using email, traditional texting and the WhatsApp-style app WeChat, which are all monitored by the Chinese government.
They can also communicate with less concern for the potential expansion of the so-called Great Firewall of China, which sees many popular sites and services blocked on the mainland.
Keen to avoid any interference, people in Hong Kong have helped downloads of Bridgefy surge by almost 4,000% in the past two months, according to analyst company Apptopia.
Bridgefy co-founder and chief executive Jorge Rios told Forbes: “We’ve seen more than 60,000 app installations in just the past seven days, most of them from Hong Kong.
“People are using it to organise themselves and to stay safe, without having to depend on an internet connection.”
Mr Rios told the business news website that similar spikes had been observed in the wake of natural disasters, when apps that require an internet connection or signal are not an option.
Others use it for more everyday situations, such as poor mobile reception at a music or sports event.
The Hong Kong protesters are no strangers to using unorthodox digital solutions to organise themselves, having also reportedly used the popular game Pokemon Go to communicate.