when a video intercom connects to a calling system there is no need to get a chime relay or button for bell because in sip protocol you can get more of this.yeah.. 2301 has poe.. found it also a few days ago. also discussed in another thread here.
All old VTO can be used as standalone, no need for display. You can register the app directly.
Only problem is, that you cannot add a chime to it. Dahua dont want to link the relay in the firmware to the button press.. always the chinese favour of a half perfect device. They are obsessed with it for some reason.
but in standalone access controllers like ASI1212D i saw a bell wire and a button for it.