On Saturday, shoppers at an Ikea in Shanghai, China ran for the exits after authorities quickly locked down the building after COVID-19 contact tracing led them to the store. From CNN:
In a press briefing Sunday, Zhao Dandan, deputy director of the Shanghai Health Commission, said the "store and affected area" would be under "closed loop" management for two days. People inside the loop must undergo two days of quarantine and five days of health surveillance[…]
Relying on mobile technology and big data, the Chinese government uses a color-based "health code" system to control people's movements and curb the spread of the virus.