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

It is possible that your phone number and confirmation number stay in the same space-time grid (the range is 800 m * 800 m) for more than 10 minute.

Space-time companion is an epidemic prevention concept vocabulary. When the personal phone number and the confirmation number stay in the same space-time grid (the range is 800 m * 800 m) * * for more than 14 minutes, 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 time, the individual's green health code will become a yellow code with warning nature, and the telephone number and confirmation number will stay in the same space-time grid (the range is 800 m * 800 m) 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) will conduct a preliminary examination and submit it to the county (city) level CDC. Those who meet the decoding conditions will be decoded by the county (city) level CDC.