Equilateral triangular structure, triangle-based with three triangular sides, preferably of aluminum components (bars or flexible foil, or at the least, an aluminum apex), 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 labeling summarizes its many applications:
BODY AND RESISTANCE BUILDER,
BLADE AND BRAIN SHARPENER,
WATER ERNYGIZER FOR HEALTH AND PLANT GROWTH,
CHEESE AND SALTED EGG MAKER,
FOOD PRESERVER AND
BATTERY CHARGER, ETC.
(REGISTERED: PIDI NSTA)

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.

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 a triangle contraption on their heads.

Definitely, urban-fringe. With no recent sightings.