How do I know when Google hits my site?

My favorite way to track this is to use a default 404 file not found script that tracks access to robots.txt.

My experience has been that Google sometimes visits sites without using Googlebot as the user agent. However, they always seem to check for robots.txt. I know this because I track the IP and I can reverse trace the IP address back to Google.

http://www.nirsoft.net/utils/ipnetinfo.html

What I do is create a script that will handle all 404 - file not found requests. When I detect that the requested page is robots.txt, I write this information to a file.

I can use this information for creating cloaked pages (which I think are old school and I don't do anymore) or I can use this information for learning about how google visits my sites.