From Pixel2 in 2017 until Pixel4, the user must press through. cellphoneSide buttons to start Assistant, or shout "Hey Google" hot word calls, or the bottom corner of Android 10 can slide up, the method is quite many, but always not so convenient.
It is important for the mobile operating system to easily and continuously invoke voice assistants because the continue conversation starts only after the assistant is active. To provide an easy way to start Assistant without hassle or sound, Pixel 4 and Pixel 4 XL will support picking up phones and talking directly to aides.
It is important to note, however, that orders must be issued immediately after picking up the phone, or the system will ignore it for privacy reasons after a period of time.
Picking up the phone and giving the order is obviously much more straightforward than pressing the side of the phone, which makes the voice assistant feature closer to being always available in the background.