Photo taken on June 3, 2020 shows the contact-tracing smartphone app "StopCOVID" on a mobile phone in Paris, France. French government launched on June 2 "StopCOVID," a contact-tracing smartphone app that could warn people voluntarily using it if they come into contact with a COVID-19 carrier. (Xinhua/Gao Jing)

Photo taken on June 3, 2020 shows the contact-tracing smartphone app "StopCOVID" on a mobile phone in Paris, France. French government launched on June 2 "StopCOVID," a contact-tracing smartphone app that could warn people voluntarily using it if they come into contact with a COVID-19 carrier. (Xinhua/Gao Jing)

Photo taken on June 3, 2020 shows the contact-tracing smartphone app "StopCOVID" on a mobile phone in Paris, France. French government launched on June 2 "StopCOVID," a contact-tracing smartphone app that could warn people voluntarily using it if they come into contact with a COVID-19 carrier. (Xinhua/Gao Jing)

Photo taken on June 3, 2020 shows the contact-tracing smartphone app "StopCOVID" on a mobile phone in Paris, France. French government launched on June 2 "StopCOVID," a contact-tracing smartphone app that could warn people voluntarily using it if they come into contact with a COVID-19 carrier. (Xinhua/Gao Jing)