China is fighting the coronavirus with a digital QR code. Here's how it works

Imagine your daily routine being entirely dependent on a smart phone app. Leaving your home, taking the subway, going to work, entering cafes, restaurants and shopping malls — each move, dictated by the color shown on your screen. Green: you're free to proceed. Amber or Red: you're barred from entry.

This has been the reality for hundreds of millions of people in China since midway through the coronavirus crisis — and it could yet stay that way for the foreseeable future, as the country battles to recover from it. Relying on mobile technology and big data, the Chinese government has used a color-based "health code" system to control people's movements and curb the spread of the coronavirus. The automatically generated quick response codes, commonly abbreviated to QR codes, are assigned to citizens as an indicator of their health status.

Although authorities have yet to make the health codes compulsory, in many cities, citizens without the app wouldn't be able to leave their residential compounds or enter most public places. Three months on, with the virus largely contained and lockdown measures gradually lifted across most of China, the small square barcodes have remained in place and are still ruling people's lives.

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