A marvellous explanation for Geeks but suppose I’m 77 yo and can’t understand geek. What can tou do with this little wonder? Why would I want one?
You can a LOT with these little devices. The ESP32 even has WiFi & Bluetooth.
What would be some examples?
For 1, the NTP clock I suggested Irv build as part of an instructional video. Obviously, the 2 lamps @Geit built. It could be used to create applications that do things on the Internet for you, like retrieve emails. There are tons of other uses.
How do you pair it with whatever you want to contro;? I’m having a hard time imagining the procedure.
The lamps are NTP clocks, too. It is basically the GiantClock code just with other animations and output. When adding a sound module you get e.g. a free hour/30min gong of your choice. 
I could add a clock face for the ring, but since the LEDs are inwards it would be hard to read and makes no sense.
It could be an interface to other devices in your network, like an wifi extender, but the main feature pool comes from soldering wires to the pins to read sensors like buttons, humidity or temperature or set pins to switch relays, which then e.g. turn on/off mains power.
By adding a clock component you can have more or less unlimited timing possibilities. I programmed mains adapters using the tasmota firmware and now for example my soldering station turns off after two hours. Same for the light switch on the guest toilet, which turns off the light after some time, because I usually only notice the light it still on days after the guests left. The four additional tubes above my workplace also turn off after two hours to save power.
All these are voice controlled, so I can turn them on and off with a simple command. This is very helpful. When coming home carrying a crate of food, I can turn on the lights in the entrance and kitchen before even getting close and use a hand.
Or if I leave the kitchen with a meal and a beverage in both hands I can turn of the light using my voice.
More or less all lights in my house are controlled by these little computers. When I am not around, I switch them in a mode, where they simulate I am home by turning lights on and off like I am moving around. These are using a random component, so the lights are not switched at the same time every day, but within a 15 minute window. This 15 minute window itself gets moved every day using sundown/sun raise as reference, too.
And before you ask: If something goes wrong I am still able to use the physical switches to use the lights, even when the network and/or Alexa is down.
Can any voice activate the lights? I would presume so. What about your door lock?
Yes, every light can be controlled by any voice. There is an option to personalize the voice, but this would only result in more personal data stored at some amazon server.
My long therm plan is to replace the Alexa system by a complete offline system running on a Raspberry Pi. Such systems exist and get better every day.
Currently, when I ask Alexa to turn on the light, the voice pattern gets transferred to Amazon, where the action gets transferred to Phillips, which then returns the signal to my home network to activate the light. The goal is to remove this sometimes unreliable external server mess, by a local setup.
I would never use a voice system for a door. Some NFC tag yes, but only when having the IoT system running in a separate network without any internet connection to avoid hackability.
Yes. I have zero IoT devices, and have zero plans to get any.
Was that an IoT device in Ali Baba and the Fourty Thieves? “Open Sesame”
The devices I use just need a single switch to be turned off in their web interface and the only thing they continue doing on the internet is getting the time. Well, until I tell them to use the local router to get the time information from.
Great write up! What tolerance did you use for the ring support? I am more of an art program person. I learned Freecad enough to be functional and hated every minute of it. Would need to return to learning vids repeatedly. Finally turned to Blender. It works much more like my brain.
I used .041 for the connection point and 0.81 for thickness, so the contact point is only one layer wide. I usually use 0.1mm tolerance for inserts per contact points. So a lit of a box would be 0.2mm smaller than the box, but here I the weakness comes from the single line (0.4) causing the weakpoint and the 0.8 building the wall on top. The 0.01 addition here is so the slicer won’t optimize anything and is probably obsolete, but it cannot hurt as it is below the resolution of an 0.4mm nozzle.
It may not be perfect or optimal, but got the job done.
In version 2 of my ring I dropped the connection mechanism.
The FreeCAD source files are included, so you can take a look yourself.
Version three is about to be real and looks fantastic.
Codename: Halo! Don’t know why 
Here to compare with the V2 (The left one). Same effect running and the same orientation:
When turned off the Light is just a white ring:
Beside the power cable there are no electronics visible at all.
What filament did you use this last one?
Noyes transparent ABS and Noyes wood color ABS for the socket.