Auto Disconnect or Auto Block When Network Not In Use

I want my Firewall Software to automatically switch to "Block Everything" mode any time I am not doing something that requires internet access.  The network interface could be completely disabled and therefore the firewall could be "sleeping".  Then if I check email or open a URL, the connection could be opened (un-blocked) until a specified idle period passes and it closes.  There is no reason to have the firewall processing traffic if I am not using the internet.  This seems like such a simple function that would reduce the possibility of un-wanted intrusions.  NIS has a manual "BLOCK TRAFFIC" function, but it only blocks TCP traffic and actually allows file access.  But is is NOT automatic anyway.

 

I have an older version of NIS (NIS 2004) so perhaps this function has been addressed in a new version.