USSD is a code parameter set by operators, namely unstructured supplementary data service, which is a new interactive data service based on GSM network. When you use the mobile phone keyboard to input some numbers or symbols preset by the network, such as * #, and then press the send key, you can send an instruction to the network, and the network will choose to provide the required services according to the instruction.
*#06# You can check the serial number of the mobile phone.
*# 1234# Hardware code and mobile phone version can be inquired.
*#6776# You can query the mobile phone version and factory information.
* # * # 4636 # * * You can check the battery usage and temperature, and change the network type.
*#800# Assertion switch (don't press it at will, or it will restart indefinitely)
*#80 1# engineering mode switch
*#802# GPS scanning test
*#803# Wireless LAN Settings
*#804# Automatic Network Search
*#805# Bluetooth test
*#806# Automatic Aging Test
*#807# automatic test
*#808# Manual test
*#809# Echo test
*#8 1 1# OTA switch (official version only)
*#8778# Always clear (reset the phone)
*#888# Check the firmware version
*#99# On/Off screen is always on.
*#900# Bluetooth on
This answer applies to all OPPO models.