Here's the reddit thread where I sourced it from and relevant information (poster has been verified as being in China)
https://www.reddit.com/r/China_Flu/comments/febv3t/what_its_...
Public areas would take your name and phone number before allowing you to enter, in the event someone there later was determined positive, they could contact you and find you quickly. This moved digitally in QR code based systems, were you would scan various locations, buses, taxis, subways, etc. and be able to be contacted and located quickly.
Then that wouldn't really be a public area, would it?
Many people, especially older ones who may use feature phones, don't have devices which handle QR codes.
Ditto for children, who may be allowed to go to public areas on their own, but don't have a QR-enabled phone.
A few years ago I left my phone in the taxi on the way to the airport. I didn't have a phone for a couple of weeks. Or, what if your phone or battery died while you were out?
Some people don't like the tracking already done and available. This takes it to the next level by making location tracking mandatory.
What benefit is there to participate? Wouldn't the majority of those people prefer to enable location tracking on their phone instead of manual QR checks?
Suppose there are multiple such systems, each with different sets of users. Someone's infected while at a train station, and only 25% of the people are contacted. Should those who are not contacted feel safe? Or extra worried, compared to how they would have reacted for having no such system?
As I wrote: "What benefit is there to participate? Wouldn't the majority of those people prefer to enable location tracking on their phone instead of manual QR checks? "
If most would prefer automatic GPS tracking over manual QR checks, the what you're proposing would result in multiple systems and incomplete coverage both for users and for people who would set up the QR codes.