After learning the appearance, location, and use of telephones in the Roaring Twenties, I stumbled into a related question: How did police officers communicate with each other and with their headquarters while on duty? I needed to know how my policemen characters handled this.
Of course, police stations had telephones by the Twenties, but policemen didn’t. The first two-way police radio wasn’t introduced until 1934 (in Boston), so they didn’t have radio contact with one another either. They could–and did–borrow a phone from a business or private home if one were nearby, but that was unreliable.
Call boxes provided the police with a direct line to headquarters. These lines did not go through the usual commercial switchboard, but connected directly to the station house. They were first installed in Washington, D.C. in 1883 (not long after telephones were invented) and proved popular with the policemen and public alike. Soon Chicago, Detroit, and Boston had them.
Because my novels are set in Hollywood, I focused on the Los Angeles police department’s communications. The LAPD installed call boxes in 1903. Before that, officers had to go to headquarters on foot with a message, or headquarters had to send a runner to find them. Call boxes let officers check in at intervals, using a key to unlock the box. Later—probably in the Thirties—dial telephones replaced the direct lines. And much later, walkie-talkies made call boxes obsolete.