I didn't take public transportation. Why did China Mobile send a message saying that I am in the same space with COVID-19 patients and need nucleic acid identification?

Your phone number and confirmation number may stay in the same space-time grid (the range is 800M*800M) for more than 10 minutes.

Space-time companion is an epidemic prevention concept vocabulary. When an individual's phone number and confirmation number stay together for more than 10 minute in the same space-time grid (the range is 800M*800M), and the cumulative stay time of any number in the last 14 days exceeds 30 hours, the found number is a space-time companion number. At this point, the individual's green health code will become a warning yellow code and be marked as ". The phone number of and the confirmed number stay in the same space-time grid (the range is 800 meters * 800 meters) for more than 10 minute.

Changsha CDC requires that if the health code turns yellow, it needs to be tested three times within 7 days. If the result is negative, you can apply to the community (village) to cancel the yellow code. After receiving the decoding application, the community (village) conducts a preliminary examination, and submits it to the county (city) level CDC after passing the preliminary examination. If it meets the decoding conditions, the county (city) level CDC will decode it.