In case of local emergencies, the scanning site codes of the confirmed patients and secret contacts can be recorded, and other people who have scanned the site codes can be correlated in time and space, so as to promote local authorities and relevant departments to carry out accurate retrospective investigation in time. In the process of using place code, the traditional manual registration method is easy to expose people's personal information, but the use of place code can fundamentally reduce the transmission level and the number of people handling personal information, and reduce the pressure of personal information security protection in the process of prevention and control.