Take a screenshot of your boarding code and print it out with a printer, which is the paper version of the boarding code. Many elderly people use old man-machine instead of smart phone. In order to take public transport, they can't check their boarding codes on the spot, so they can only register their boarding codes with their children's mobile phones, and then take screenshots and print them out with a printer in advance so that they can check the backup when they pass the security check.
The trip code has four colors, namely:
1, green: the travel code is green, which means that your current environment is safe, and you are not a suspected patient or close contact in COVID-19.
2. Red: The travel code is red, which means that you are a confirmed patient in COVID-19 and a suspected patient in COVID-19.
3. Yellow: The trip code is yellow, indicating that you have been to a medium-risk area.
4. Orange: The travel code is orange, which means that you are a close contact of COVID-19.