I'm trying to create an email alert to notify the case owner when I ticket was modified by someone other than them, but not the system owners which are automated processes.

I've tried this, but it still sends an alert when the case owner modifies their ticket.  Any help would be greatly appreciated.

AND( 
OR( LastModifiedById <> OwnerId, 
LastModifiedById <> 'systemowner1', 
LastModifiedById <> 'systemowner2' 
))