A normal, physical doorbell is 24/7 connected to electricity, else it wouldn't work. It typically has no surveillance capabilities, except when used, it makes a sound/signal/buzz. That's typically its purpose.

A 'smart' doorbell [meta: I hate this terminology, and will just call it 'doorbell camera' for the rest of this post] needs electricity in order to do the very same, but it also serves another purpose: record (via camera and microphone, and sometimes other sensors ie. IR camera). This recording of data can be stored, analyzed, etc. For example, you can perform ML on the feed to detect dogs, you can do data analysis on it for example when postal service usually arrives, you can record postal service stows packages away in the premises, etc. In order for it to be analyzed, it needs networking capabilities (wired, or wireless). Doorbells need to be serviceable, so they can typically be dismantled from the outside. Wired and wireless can both be MITM'ed, and DoS'ed. If that happens, you want the feed to be recorded as much as possible, in order to record the attacker. You also want to secure your feed. In order to MITM or DoS a wired doorbell, physical access is required which is why a wired doorbell is superior IMO.

There's no need for your camera to have internet access. Some ports have to be accessible from your NVR; that's it: you need to be able to update the firmware (e.g. to protect against vulnerabilities such as KRACK), and you need to be able to record your stream (e.g. access the RTSP stream). A speaker or screen can be useful to communicate with a visitor. Your NVR can manage all of this, and so can you (usually via a reverse proxy with internet access, but we shouldn't neglect authentication here). The doorbell camera itself doesn't need such. It does, however, need some form of networking capabilities.

So what I do: apart from having it in a separate VLAN, I record my feed, and immediately store it locally (on-prem) and remotely (via adequate internet access; in my case, not in cloud). However, my doorbell camera is connected via Wi-Fi. This is where the story e