In the first beta version of Android 11 found a feature that performs some action after a double tap on the back panel. Among them: start the camera, open the application, activate Google Assistant and mute.
This feature has already been launched on Pixel 2 XL and Pixel 4 XL. It does not require a special sensor, just a gyroscope and accelerometer.
It is not yet known whether other Android smartphones will get this option. It is quite possible that it will be an exclusive Google Pixel, like Active Edge touch panels. In addition to the camera, you can run other applications and mute.