Maybe I don't understand you fully, but you mean your problem with the Dahua VTO's is that the actual press of the
doorbell button on the VTO does not register like a IVS/tripwire (etc.) event on a normal camera would?
I have no experience with the Dahua VTO/VTH's, but I always thought pressing the doorbell button on those VTO's would register just like an IVS event would.
For example, if I would connect the VTO to my Dahua NVR (and record it's camera feed 24/7 and IVS etc.), a doorbell press would show up on the playback timeline but apparently it doesn't?