Many thanks to the YouTube algorithm for suggesting the short that was the teaser for "How I controlled ESP32 5x5 matrix lights with my phone" by CMoz. That video's great and it leads to the project video 3 Minutes Wearable Necklace You Can Control With Your Phone. I think https://github.com/cmoz/dazzle5x5ESP32C3 is related.
It's great that CMoz has a Tinker Tailor website and a book "The Ultimate Guide to Informed Wearable Technology".
I wish there was a buy everything you need for the necklace button. Hopefully I'll come back to this soon. It may take 3 minutes to assemble the necklace, but the whole thing will take me longer to find the parts, buy them, setup and walk through the tutorial...