To find out, there is a simple tool by Google, which works well. But the disadvantage is that you have to throw all you data into the kraken before you get some tiny information back.
An alternative is piwik. By using this open-source tool you can detect, save and evaluate the attendance on your own server.
The installation is as easy as the installation of wordpress:
- Download the zip file and unpack it
- copy the unpacked folder to your favorite Server (with MySCL and PHP)
- start the script for installation and set up Piwik
- paste a short code on any page, that should be tracked. As an alternative, there already is a complete plugin for wordpress.