IFERN or Interagency Fire Emergency Radio Network is (in my opinion) one of the best interop systems around. The actual frequency is 154.265. That frequency is being patched into your EDACS system on a special talk group. Because the county's antenna for the VHF frequency is so high, it is picking up activity from long distances away (as here in Illinois). We have a consolidated dispatch system here in Illinois called DuComm. They have a dedicated UHF frequency that passes through radio traffic from IFERN. It is common for me to hear box alarms in Wisconsin.
Basically if a local fire company has a large incident (say a structure fire, MCI, Hazmat, etc) the "command" on-scene chief can call the local IFERN district on the IFERN frequency to ask for assistance from neighboring towns. The district office has box cards that would determine who should respond and with what equipment (if available). A "box" or incident number is established and the district would put out a common set of tones on 154.265 to alert all towns, dispatch centers, PSAPS, etc of the box alarm and the requested response.
The tones are common (1082hz / 701hz) across the entire area (the same for Illinois). Local towns that need to respond then dispatch on their own frequency. Enroute equipment then switch to 154.265 to talk to the district office to state their response. When on-scene, the command would most likely have them switch to one of the common fire ground channels. If the situation worsens, command may ask for elevated box alarms which then call for more equipment and personnel from further away. When incidents are minimized, command will ask the district office to "strike" the box alarms and will advise what equipment can be returned to their respective stations.
I have lived in may states across the country. I have seem many circumstances where towns and equipment don't know how to communicate with each other (especially when they run solely on separate trunked systems. I have seen personnel that don't know what mutual aid channels to use. As I stated, the IFERN & MABAS system has got to one of the best interagency systems that really works.
As for listening with your own antenna, just get a good VHF receiver and program it for 154.265. If you have one of the Uniden scanners that have the FTO (Fire Tone Out), you can program up on the IFERN frequency and tone set. Then you can have your own alerting system. However you are lucky that Ozaukee County has dedicated a TG for this frequency already. Their will probably receive much further than you probably will so you can just monitor that.
If you want to read up on how Illinois does their system, check out MABAS.ORG .
Hope this helps you.