The Attached File is an example of the sound that I hear when a Police Officer presses the emergency button on his/her radio, and the Radio sends an MDC Emergency packet, then the Dispatch Computer automatically sends a MDC Emergency ACK packet to let the radio that sent the emergency that the emergency was received. It then has the Officer's Radio transmit constant for about 30 seconds or so. If the dispatcher wants to talk to other units, she can override his transmission (it is a repeater system).
In this clip she is trying to get the status of the officer that hit the emergency button. It is somewhat pointless because his radio is transmitting automatically and he/she couldn't hear the dispatcher talking, unless the officer was in his car and hit the emergency button on his portable (he then could hear the dispatcher on his mobile), or he hit the mobile emergency button and could hear it on his portable. But it does make sense, because if he doesn't respond on another radio, that means either it was accidental and he didn't know he hit it or it is a true emergency.
You can hear the alarm in the background that the dispatchers hear when an emergency is received. This is after she tried to make contact with the officer that initiated the emergency alarm, but was not able to. So far, for as long as I have been listening (almost 2 years), they have always been accidental in my town.