Alipay, search for "peer self-examination" in the search bar above, and click "Query Now" in the peer self-examination of the Citizen Center to conduct self-examination. The function of self-checking code is to independently detect whether it is with confirmed or suspected cases and determine the position and trajectory of peers. Together with the self-check code, there are Shandong electronic health code and communication big data travel card, collectively referred to as "three codes".