Arduino and NRF24L01

The reason behind this short learning curve:
My son likes to be shut away in his room away from the rest of the noisy family. His mum needs his presence from time to time to help with his autistic brother and meals etc. He asked me about having something in his room that would save his mum going up and down the stairs to get him and I suggested a wi-fi doorbell. Easy solution. He wanted something that was two way. No more details than that, like audio or visual. I had heard that the NRF24L01 was a very cost effective and yet effective little radio device, so I decided to do some research and see what I could come up with.
There are a number of Instructables available that show how to use the NRF24L01 radio module with an Arduino. I found that it was difficult to find a simple setup where two Arduino’s could communicate in the exact same way. I wanted both setups to each transmit and receive in the same way and that would define the most simplest way of doing both things on two Arduinos. Once I have two Arduinos communicating back and forth, I then have the basic framework to extend them to do other things.
This Instructable does not produce the product that my son wants, but does produce the framework for it and many other simple two-way applications.”