The number of Bluezone downloads has increased dramatically in the three weeks since a second COVID-19 outbreak occurred in Vietnam in late July. As of Thursday, the app had been downloaded more than 20 million times, according to the Department of Information Technology of the Ministry of Information and Communications.

The contact tracing app, developed by Vietnamese firm BKAV, uses Bluetooth Low Energy, a wireless personal area network technology that links smartphones within a two-meter proximity. The app is completely confidential, anonymous, and transparent. It only stores data on each user’s phone and does not transfer a user’s personal information or location to the system.