Since you can’t see who is watching, you should take control of what they can see. If you are worried about prying eyes, adjust your privacy settings:
The Facebook Profile Viewer is a useful tool that allows users to view Facebook profiles in a more organized and accessible way. Here's a potential development of this tool:
Here is the "story" on how both work, including what is real and what is a scam. 1. The Real Story: Viewing Story Viewers
Facebook explicitly states that third-party apps cannot provide this functionality either.