639
DuckDuckGo made sunglasses that do absolutely nothing, and they sold out
(www.techspot.com)
This is a most excellent place for technology news and articles.
Glasses that have cameras should require red led to be on at all times by law (when turned on).
I believe the Facebook glasses do have this.
The problem is just that the light is rather easy for an end-user to remove. And that it may be too dim to clearly see in brighter situations.