10-3 is an alert to all communications on that particular talk group from officers, to be silent on until further notice that it has been lifted. Only those involved in the serious nature of the call are directed to talk on the talk group. The comm center Sargent is informed of when it happens, the nature of the call, if any officers requested a 10-3 , an subsequent updates, including status calls of officers involved in the situation. This happens so the communications is not tied up with other less important calls, so the air is free in case an officer needs to transmit immediately without waiting for another to finish their transmission on the talkgroup. I have even heard a situation where an officer emergency was activated on his radio by mistake, but they couldnot reach him calling many times, so the comm center dispatch issued a 10-3 in effect, then the officer responded with his status and what was happening, and said 10-3 is not required. Theres many different reasons why it happens