@VDG24
When any of our three Google Nest Hello Doorbells is pressed, we get a chime AND an oral "Someone's at the xxxxx Door" announcement on each of our Nest Hubs, as well as a live video of the doorbell's camera. The volume depends on whatever the current volume setting is on each Nest Hub. I understand that if any Nest Hub is set to "Do Not Disturb", there is no chime or announcement on that Nest Hub, but we don't generally use the "Do Not Disturb" setting.
Since we have the older Google Nest Hello Doorbells that work in the Google Nest app, in addition to the small banner we also get a ding-dong sound on each of our iPhones; this sound is not configurable; the banner and sound are enabled under our iPhones' Settings | Notifications | Nest. The volume depends on our iPhones' current volume setting. (If my Apple Watch is on, I get just a standard ping-like sound on my Watch only.) For 2nd gen doorbells, notifications are enabled under Settings | Notifications | Google Home, but the sound is just the default notification sound. With iOS, the default notification sound can now be configured, but it applies to ALL apps using the default notification sound, not just the Google Home app.
P.S. Our indoor doorbell chime is turned off because we had to disable the "Indoor chime" option on all 3 of our Nest Hello Doorbells, since the internal battery has failed on all three and the doorbell goes offline when the doorbell button is pressed, unless the "Indoor chime" option is disabled. So we depend on "Visitor announcements" and iPhone notifications.
