This from Steve Redick:

I want to share something amazing for my fellow Chicago FD fans. This is a recording of operations in the Main Fire Alarm office in 1957 during a 3-11 fire. It came from the archives of my friend, mentor, and boss Jim Evans. The mic was open allowing us to hear telegraph signals, radio transmissions, and various phone conversations of the operators. This is an amazing piece of history … companies long out of service, fire insurance patrols, early radio operations … just amazing things. Listening to the telegraph signals alone is incredible if have the knowledge to interpret them as many of us older fellas have. I don’t know if Jimmy actually recorded this or acquired it somehow. It is a onetime opportunity to listen to history. Most, if not all of the operators heard in this recording are gone. I recognize a few voices.