Various features vary by model and manufacturer. Usually, budget models are limited to video communication and lock control. But most modern products have the ability to integrate into home security systems, connect additional surveillance cameras, record video files on command or in automatic mode, etc. Like audio, video intercom consists of an indoor unit and an external module. The indoor unit includes:

Monitor - black and white or color, size from 3 to 7 inches;
Control panel - from where the device itself is programmed or the lock is controlled. Some models have touch controls placed on the monitor;
Communication handset or speakerphone built into a monoblock;
Power source - network adapter;
Quad for connecting multiple cameras or other additional devices typical for premium kits.
The external module consists of the following devices:

Speaker;
Camera with IR illumination;
Microphone;
Control keypad for calling a subscriber.

According to the method of placing the internal video intercom module, stationary models for wall mounting and more expensive mobile devices can be divided. They have a compact base for communication and recharging and several portable control modules that look like smartphones.

I am sure that useful information about entry monitors will give you the opportunity to increase your knowledge in this area and help you make the right choice