Erny Baron's triangle is an equilateral structure, triangle-based with three triangular sides, preferably of aluminum components (bars or flexible foil, or, at the least, an aluminum apex). The triangle was purported to provide a variety of health benefits plus a miscellany of day-to-day uses. Like pyramid power, effects are attributed to harnessing of energy forces through its shape and space.
The label summarizes its many purported applications:
Body and resistance builder.
Blade and brain sharpener.
Water energizer for health and plant growth.
Cheese and salterd egg maker. CHEESE AND SALTED EGG MAKER,
Food preserver.
Battery charger, etc.

Sizes vary according to area of use or application, small enough to place over the eyes for a variety of visual complaints, or large enough for various anatomical locations for a sundry of complaints: headaches, memory loss, wound healing, hiccups, pain, etc.

During my visits in 80s, I saw many many triangles of various sizes scattered all over the house. There was always a container or two of water being 'energized.' Dead batteries were always being resurrected. I was told my father did daily doses of energizing for memory boosting.

At the peak of its popularity, as a "brain sharpener," it was a common sighting to see student groups going to-and-fro school wearing the triangular contraption on their heads.

Definitely, urban-fringe. There have been no recent sightings.