Since first appearing in December 2019, COVID-19 has spread rapidly in over 180 countries worldwide, with the death toll already exceeding tens of thousands in just a few months. A number of digital contact tracking mobile apps have been developed to effectively combat the disease. For instance, the City of Singapore has launched the 'Trace Together' app, the French government is developing the 'StopCovid ' etc.

This project uses the example of China, where citizens are required to use a 'health code' app which colour codes people green, yellow and red according to their level of health to determine whether they are passable. However, prolonged epidemic prevention and control has led some public places to relax their checks on 'health codes'. Some people have changed the colour of the 'health code' by p-charting it to ensure freedom of passage, all of which proves the huge vulnerability of manual testing and the accuracy of the 'health code'.