I have been working with House Automation since 2005 and with IT since 1969.
My interest in Home Automation came from the fact, that I wanted to be able to switch on the heating in my vacation house from home. Then I would arrive to a warm house independent of the time of the year.
Later - as i one day ran out of fuel oil - the need arrived for being able to monitor the fuel level in the tank and send me an alert when almost empty.
I have been thru many different technologies and in the beginning, I made all the software as well of hardware myself. Later i started to look for Open Source solutions where possible.
Basically all sensors, relays and the oil level sensor are connected to an OneWire bus. The fuel level sensor has been made by simulating a OneWire device using an ATTiny85 connected with I2C to a proximity sensor. See http://palsbo.com/arduino/OneWireSlave.html
A Raspberry Pi serves the following functions.
I have installed the internet with a NAT router with port forwarding for access from the world.
Bandwidth is low as the internet is delivered via cobber and I have considered to use Mobile data network (for other reasons than the Home Automation). This gives a few problems, as the Mobile data network uses shared IP which makes it impossible to reach the web server (OpenHAB2) from the outside world. The problem can be solved by moving OpenHAB2 and MQTT broker to my home network. I may also use a public MQTT broker and write an web application on a public web server, using websocket to connect to MQTT.
With the world's increasing focus on IOT the market has floated with devices usable for IOT. A common problem is, that all these products uses their own proprietary protocol and user interface (usually mobile phone apps) to access the devices (Philips a.o.).
I understand the various producers wish for protecting their customers from using other producers products, but the history have proved, that development over time will concentrate on one standard. MQTT is a easy and handy way to solve this, as it does not requre any kind of complicated port forwarding.
With IOT being introduced to alle type of equipment like refrigerators, washing machines, tv's and hi-fi equipment as well of normal house automation equipment, it is not likely that one producer will be able to supply all the needs.