How to implement an eyeglass finder

What sort of technology would let you attach something small and light and unobtrusive to a pair of eyeglasses, and then when you have lost them, home in on where they are?

I have explained various approaches I have thought of and existing commercial approaches at which is organised as a student project outline.

RFID looked promising since the tag is small, but I can’t find any technology to home in on its location.