This dialog allows you to enable/disable the serial port. In addition, it will allow you to call up the commToolbox to set such things as baud rate, port, method etc.
 
The Choose Target button tells this copy of XTension to send all XTension events to a copy of XTension on another Mac.
If you choose this button, you will be prompted to select the destination Mac and copy of XTension. Obviously you must have a network (dial-in or LAN), and another Mac.
 
Scripting verbs are provided which do this dynamically.
Obviously, the next thing you will want to do is set the target of the 'monitor' copy of XTension back at the 'master'. Thus, events on the master are displayed on the monitor, and commands issued on the monitor will be sent to the master for execution.
( see WWW.SHED.COM for specific tutorials and articles about this)
Thus you need have only one X-10 interface, which can be connected to a Mac in the closet or basement. If you have other Macs and even a simple network, you can monitor and control the 'host' from any other Mac in the house. Or even dial-in.
Using the "monitor" only mode, you might even have two or more Macs, each with their own X-10 interface in a redundant set :
One Mac can be 'master', another might simply monitor the system events, and react to a failure of the master by taking itself out of 'monitor' mode and becoming the 'master'.
The monitor might send AppleScript commands to the monitor or keep track of a specific X-10 address which the 'master' sends every 5 minutes etc. The monitor might also/or check the turn on/off of a specific X-10 address which the master also periodically turns on (via scheduled event).
By checking the X-10 event, the monitor machine might discover more subtle problems earlier than just the network 'ping' solution.