See simple intercom circuit using transistors and a few parts. So easy build and cheaper than ICs. For a small home and learning.
This morse code generator circuit is suitable for learning basis of communication. Unbelievably, short and long tone can be decoded into letters and text.
See Intercom circuit using LM386 and other IC. louder transistor version. And easy and cheap. With Condenser MIC and Speaker, longer cable.
A simple fiber optic intercom communication systems to home use. Video Door Phone Intercom is going to happen in the future. or Meetings monitor route.