In China, authorities are using technology to track who is likely to be healthy -- and who poses a risk.
Residents are each assigned a color-coded QR code on their phones -- and that color correlates to what they're able to do. In Wuhan, even now the lockdown is lifted, residents still need to produce a green QR code to leave their compounds. For those returning to work, they also need to produce a letter from their employer.
To get into places such as restaurants, people need to show that QR code -- and only people with a green code will gain entry.
But if your code is yellow or red, it means you've been flagged for some reason. If, for instance, you had been on a plane with a person infected with coronavirus, you would be flagged and your code might change color.
Those with a yellow or red code might be asked to self-isolate -- or even have to go into state quarantine.
The whole thing relies on big data, and means local governments have a database of people's travel history, their health history, and whether they've been in close contact with anyone who has coronavirus.
There's another potential problem -- different provinces have their own health QR codes, and sometimes they have issues recognizing codes from another region.
Watch how the codes work here: