This is also a topic that John Naughton picks up in the Guardian:
One thing that does appear to be happening in China, however, is deployment of the state’s surveillance capabilities. At the heart of the project is the ubiquity of smartphones. According to the New York Times, citizens are now being required to install an app on their phones that dictates whether they should be quarantined or allowed into subways, malls and other public spaces. People sign up for the “Alipay health code” and are assigned a colour code – green, yellow or red – that indicates their health status. A green code enables its holder to move about unrestricted. Someone with a yellow code may be asked to stay at home for seven days. Red means a two-week quarantine.