I figured something out today. At the gym there are mirrors everywhere. So that means I can always see what everyone is up without trying. I can do the same thing with windows and a little glare. The library has a 24hr room where they allow food & drink. This room has its own entrance and big windows between us and the rest of the library. These windows catch some glare and I can see everything in the room behind me while looking at a large area of the library at the same time. I caught girls getting a second look from both directions.
In the movie Doubt, Maryl Streep tells Amy Adams to hang a picture frame above the chalk board so she can monitor the children when her back is turned. After today I think people in general are just as oblivious to their reflection as those school children.