The trip code is determined by the signal received by the cell phone.

Communication big data itinerary card is by the China Academy of Information and Communication Technology in conjunction with China Telecom, China Mobile, China Unicom three basic telecommunications enterprises using communication big data for China's cell phone users to provide free query service, cell phone users can use the service, query the information of all the cities and municipalities that I have been to in the previous seven days. As of March 25, 2020, the cumulative query volume has exceeded 450 million times.