Can I assign a function to the Android volume button? --Why Android I can't hear anymore

Yes, the volume button on the side of the Android device can be used as a "shortcut button" that can call a specific function by pressing and holding the up and down volume buttons at the same time for 3 seconds. It is not possible to assign any function / app, and it must be an app / system built-in function that supports the shortcut service, but there are many situations where it can be used.

The shortcut service is positioned as an accessibility / accessibility function, and has functions such as color inversion / color correction, TalkBack and switch access (a function that uses an external push button for operation). There is only one function that can be called by pressing and holding the up and down volume buttons for 3 seconds, and you can select the function you need in advance and call it as needed.

To change the association between the up and down volume buttons and the function, open the screen in the order of "Settings" → "Accessibility" → "Volume key shortcut", and tap "Shortcut service". The items displayed there are the functions / apps that can be assigned to the upper and lower volume buttons.

For example, if you select "Voice-to-speech conversion", you can call the voice-to-speech conversion app at any time by tapping the doll button that appears at the right end of the navigation bar to convert the spoken words to text. When you want to dictate, you don't have to start the app every time.

The "accessibility menu" is likely to come in handy for Android beginners. When you tap the doll button that appears at the right end of the navigation bar, a screen with frequently used functions such as "Recently used apps" and screenshots will appear, and you can easily operate it.

You can turn off the enabled shortcut service by pressing and holding the up / down volume button again for 3 seconds at the same time. This will eliminate the doll button on the far right of the navigation bar, and you will not be able to call the functions assigned to the up / down volume buttons.