I’m pretty sure this patent from Nokia, filed in 2001 and just approved by the US Government (and hey, what isn’t!) is talking about using a simple radio frequency detector to light up an LED indicator on a pair of glasses and not anything more fancy than that. That would make it easy to tell when someone is calling you on your cellphone, but also easy to tell when anyone in the area is calling or being called, as well. The real news here is that this diagram shows the exact sort of glasses worn by Finnish engineers—it’s not pretty. (Thanks, Daniel!)
Ancillary wireless detector [USPTO.GOV]
