Space-time companion number means that my phone number and the number of the confirmed patient 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, and the found number is the space-time companion number. My green health code will turn into a yellow code with warning nature, and will be marked as a space-time companion by the system.