It's quite easy technically but a bit of a faff with the wiring and connections if it's not familiar to you. I would use the AcuSense DS-2CD2346G2-ISU/SL. It's on my list of things that I don't need but feel the need to do....On completion, pressing a standard door bell push would:
- sound the chime as a normal doorbell - nothing fancy there
- simultaneously trigger an alarm input on the camera, resulting in a push notification to your mobile via Hik-Connect
- the camera specified can be used for two way communication via Hik-Connect when the input is received if you're not home
- the Hik-Connect notifications list shows you thumbnails of every time the doorbell was pressed for quick review of who's been to the door while you were out. Those events could also be easily reviewed on the NVR
The bell push would be used to switch a 12V DC supply to energise the coil of a double pole relay. One pair of the relay contacts would be used to trigger the chime, while the other would be connected between the cameras alarm input and ground. If there was already a standard wired bell push and chime in place that could be used.
The benefit of doing it this way is that you don't need an additional intercom/doorbell camera or monitor - just a camera that is close to and has a good view of the door. I already have that camera by my door but I reckon I could set the above up on an existing wired doorbell spending no more than £20. When I get around to completing it I'll post on this site.