Just put in the control channels into the scanner for your area. I think you use ID scan then (someone correct me if I am wrong). Might be ID search. I have a 396T and this is how I did it on that. Now with the 436, I just put in my zip, select services, and listen to everything in my area.
in the data base (armer system) for your county,there are frequencies listed in blue. these are the possible control channels for the system. they are blue because they change (probably every 24 hours)
one of them will have what sounds like a diesel motor on a high rev.
that is the control channel.