(WUHAN, China) — Since the coronavirus outbreak, life in China is ruled by a green symbol on a smartphone screen. Green is the “health code” that says a user is symptom-free and it’s required to board a subway, check into a hotel or just enter Wuhan, the central city of 11 million people where the pandemic began in December. The system is made possible by the Chinese public’s almost universal adoption of smartphones and the ruling Communist Party’s embrace of “Big Data” to extend its surveillance and control over society. Walking into a Wuhan subway station Wednesday, Wu Shenghong, a manager for a clothing manufacturer, used her smartphone to scan a barcode on a poster that triggered her health code app.