There are a number of different video doorbell is on the market and the two most popular are Ring which is owned by Amazon and Nest which is owned by Google.
If somebody presses the doorbell it can be programmed to appear on your Alexa Show, if you have a smart doorlock you could unlock it for them.
It is also very useful if you are away as the doorbell can appear on your phone so if it is delivery you could ask them to leave it with the neighbour
The Nest camera features automatic intelligence that recognises peoples faces and can tell you who is ringing the doorbell, you can check when people have arrived and left the house which would give great peace of mind as a family member could check when carers arrive for example.
The doorbells can also be integrated with other camera systems for inside and outside the house, this can all be accessed remotely via mobile phone or internally using Alexa devices giving great peace of mind and added security.
For example you may see that someone has fallen and you could raise the alarm.
Below are a couple of videos showing what features are available