Emboldened by their successes in stamping out Covid, Chinese officials are turning their sharpened surveillance against other risks, including crime, pollution and “hostile” political forces. This amounts to a potent techno-authoritarian tool for Mr. Xi as he intensifies his campaigns against corruption and dissent.

The foundation of the controls is the health code. The local authorities, working with tech companies, generate a user’s profile based on location, travel history, test results and other health data. The code’s color — green, yellow or red — determines whether the holder is allowed into buildings or public spaces. Its use is enforced by legions of local officials with the power to quarantine residents or restrict their movements.

These controls are key to China’s goal of stamping out the virus entirely within its borders — a strategy on which the party has staked its credibility despite the emergence of highly contagious variants. After China’s initial missteps in letting the coronavirus spread, its “zero Covid” approach has helped keep infections low, while the death toll continues to grow in the United States and elsewhere. But Chinese officials have at times been severe, isolating young children from their parents or jailing people deemed to have broken containment rules.