In my county the emergency vehicles are all tracked via gps via mdt so the mobile radio panic buttons automatically send the police to all police vehicles along with a ambulance depending on the nature of the call the officer is out on at that time. All Ems units automatically get the police and if it is a paid Ems unit which are usually als hospital based the Ems supervisor for that health system responds. Fire vehicles get Ems and police. For portable radios the response is the same if the unit is on a call if it is a individually assigned portable they page the unit with an attention tone if no response after three tries they contact the chief officer.