NECLUMI is the first projection-based interactive necklace. In their own words:

At the current stage the whole setup is based on iPhone running custom app and a pico-projector connected via HDMI cable and attached to the wearers chest.
Given the rate of miniaturization of the pico-projector technology and observing the trend of wearables treated more as jewelry and fashion accessories rather than just gadgets, we predict that wearable projection and projection-based jewelry become a reality in a few years.

The project was done with visual media collective panGenerator and the authors are currently committed to create a standalone version of the project with additional funding and collaboration. Awesome work!