So, what area is it that you are trying to listen to ?
Just to clarify, need your location(city, county, state), and the things you want (cops and stuff pretty vague). The usual is State and local Police, Fire, EMS(ambulance and medical helicopters), but some are not interested in EMS, but may want Emergency Management(local FEMA) that handles toxic spills, floods, or other disasters.
It would help greatly if you would go into your User CP (found in the blue toolbar under the thread title) then click on Edit Your Details in the left frame. Put in your county/state. This will help narrow down your responses to those folks that are in your general neck of the woods