Just a note for people that want to go fully offline regarding the two-way audio feature, I suggest looking into Amcrests View Pro app for android and Amcrest View Lite for apple devices. It uses ONVIF to connect to the doorbell and supports the two-way audio.
I have two devices: an old Nook HD with LineageOS installed, running Amcrest View Pro and iPad 1 with a Amcrest View Lite from the AppStore. Both of them along with the AD110 are on my IoT VLAN with no internet access and working fine.
As a precaution, I would if you are using the apps, do NOT modify any of the doorbell properties using them. Just use them to view and have two way talk audio.