When I'm listening to Sac Pd on certain calls, seemingly the ones with firearms involved, there is an intermittent beep. I can hear officers ask to start or code 4 it. Is this some kind of alert to keep a channel clear for this particular incident or what? I've been trying to logic this question to death; now I just want to know whats what. Thanks
The technical term is Air Clear Marker.
When activated by a dispatcher it means, priority traffic only. It is mostly used when radio traffic needs to be minimized for a specific incident. Some agencies have policies to use it to minimize radio traffic to allow the dispatcher to catch up with their computer tasks.
Most often the marker is used when officers going on scene to a robbery alarm, fight in progress, checking the inside of a building with suspect inside, vehicle that has failed to yield, etc.
Any officer just tuning in is alerted to the beep, meaning to only transmit if related to the active event or he/she has priority traffic.
Officers are trained to pause and listen for the air clear marker before they transmit.
Some dispatchers have the ability to "tone" out to alert officers or to simply get a specific officers attention. You'll hear beeps sometimes just prior to a robbery alarm or shooting call. Sometimes when an officer fails to answer on the radio, you'll hear a tone out in attempt to get them to listen to the radio.