I just read an article in a magazine about data over sound.
Some apps use ultrahigh frequency sound to commuicate with other devices without being recognized. This works even if the device is in Aeroplane Mode since it only uses microphone and speaker.
You can control the microphone on android, but you can’t control the speaker so every app can use your speaker to send out data without you recognising it.
I’m not really sure how /e/ can handle this but i think it should do.
I have an idea: There are numerous Audio Equalizer apps for Android. If you simply chop the spectrum at (or slightly below) the upper end of your actual hearing, then the only sounds the phone can make will be sounds that you can hear and know about.
It’s still possible to communicate very slowly using other sorts of sounds that would fall within the audible range but be imperceptible, but I’ve never heard of apps doing that. A partial solution there would be some sort of visual notification that a given app is playing sound, and if that appears unexpectedly, you know something’s amiss.
it’s at least one of the issues, where android 9 introduced some privacy related improvements:
Limited access to sensors in background
Android 9 limits the ability for background apps to access user input and sensor data. If your app is running in the background on a device running Android 9, the system applies the following restrictions to your app:
Your app cannot access the microphone or camera.
Sensors that use the continuous reporting mode, such as accelerometers and gyroscopes, don’t receive events.
Sensors that use the on-change or one-shot reporting modes don’t receive events.
If your app needs to detect sensor events on devices running Android 9, use a foreground service.