RealTimeSync with 2 conditions

[52ROSt]

I am running Linux Mint 17.3 on a notebook.

Using FFS, I want to synch my /home folder with a copy on an external HDD. Synch setting "mirror" my /home with a folder /homecopy.

Conditions:
1 - Notebook is in the docking base, which means the external HDD is connected
AND (not logical or)
2 - Any file or folder in my /home (internal HDD in my notebook) has been changed

My Linux command capability is not good enough (yet) to create a LInux script and place it into the required folder.

How does the script need to look like?
In which folder must the script be located?
Other things to be considered?

Thanks in advance for your help!