How would that backdoor be activated?

See, phones could be preloaded with a malware that make it so that it doesn’t actually turn off radios (like wifi bluetooth or celluar) when you change the settings, and only stops transmitting and goes to passive listening only. Once they detect a certain signal, like when police activates it in a protest, the phone then activates and disables recording, and maybe also disable trasmission of data.

I mean this is just hypothetical. I don’t know if they are doing this, or if they can. But like when you think about it, its quite possible.

There are already reports of malware that fakes a shut down animation and silently records in the background, and execute remote commands.