MIUI has a lot of secret settings inside that are left out of the system but were found after the Xiaomi Community to use for the people who know how to use them properly. Those dialer codes must only be used if you know what you are doing. Xiaomi keeps these features open for the reason being, the people who know this stuff to test how the phone operates, and if there is a bug to report. Those MIUI secret dialer codes are meant for testing purposes only.
60 Android Secret Codes – Hidden Menu and Dialer Codes
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