Calling All Cars

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10:40 p.m. “I got about 2,000 college students coming from Walnut Street to 30th to Center City.”
10:46 p.m. “It’s endless, chief. Endless.”
11:11 p.m. “They’re on top of trash trucks. There is to be no one on top of trash trucks, guys.”
11:14 p.m. “We have multiple people on Broad Street swinging on light poles.”
11:20 p.m. “Climbing the trash trucks at 13th and Market.”
11:25 p.m. “I need to get the fire extinguisher out of my trunk. I got a fire on Broad Street just south of South. Someone lit a Christmas tree on fire.”

Philadelphia Police radio transcripts after the Eagles won the 2018 Super Bowl

Do you remember the old movies from the 1930s when a radio in a police car would blare out "Calling all cars! Calling all cars!" The diligent policemen would zoom away in their car with the siren screaming. The dispatcher had no idea if the radio cars heard the frantic call because two-way radios were uncommon and expensive. So from the late 1920s until after World War II, most police departments relied on their cruisers having radio receivers only. Today, police use digital radio systems that carry data, video, and other information.

Police have been perfecting electronic communications since just after the Civil War. In 1870, the Chicago Police Department installed call booths around the city that contained a modified telegraph system. The beat cop would move a pointer around a dial to select one of a number of situations like "thieves," "arson," etc. and pull a handle. This would automatically telegraph the officer's needs back to headquarters. When telephones came along, HQ could now alert policemen in the field via lights installed around the city signaling them to phone in using "call boxes." Call boxes are still maintained in some major cities today. Here's a "what's old is new again" fun fact: many colleges, the University of Kentucky included, have lights around campus that flash to alert when there is an emergency.

The 1920s saw a dramatic rise in crime. After all, this was the Prohibition Era and cops had to bust up stills and raid speakeasies. In response, the Detroit Police Department began developing a central dispatch transmitter that police officers in the field could receive on car radios. In 1928, Detroit PD launched the radio station KOP (clever!) for one-way police communications. Police units basically just monitored the radio for their car number to be alerted. The "Calling all cars," phrase was used to summon all available units to a particular crime scene.

During the depression money got scarce, and banks got robbed. Police not only had to get to the scene quickly, they needed to contact other cruisers to be on the lookout for a Ford V8 with a man and woman speeding their way. Two-way car radios first started appearing in 1933, but could cost more than the car itself. Advancements during WWII made them more affordable and compact. By the 1960s, most police departments around the country had some sort of two-way communications.

In larger cities, the sheer number of radio cars on the road jammed the noisy AM band. New FM bands were opened up in the VHF and UHF spectrums allowing crisper and cleaner communications. Cities such as Los Angeles employed separate dedicated HQ and patrol car frequencies. As Americans learned through such procedural cop shows as Adam-12, dispatch occupied one radio channel, and radio cars occupied separate channels. Patrol cars could not hear each other unless they switched to a tactical, or "tac" channel for car-to-car communications. To hear dispatch, they had to switch back to the main channel. Later in the 70s, LAPD cars had a second dedicated receiver and speaker to hear dispatch no matter what channel they were on.

In the 80s, communication once again got a kick in the pants with Mobile Data Terminals (MTS) that put keyboards and computer screens in patrol cars, cutting down on voice communications and freeing up the radio channels. Walkie-talkies shrunk and some even did double duty as car transceivers. Today, almost every beat cop has a personal mobile unit, thanks to the small size and lower cost.

A lot of departments are moving to all digital systems for improved clarity, data capabilities, and encryption. Much like the early days of police radio communications, there are drawbacks to an all digital system. Number one is cost, but there have been a series of federal grants that smaller departments can take advantage of. The second problem is the limited range of digital transmission which requires more power than older analog systems. The third, and most controversial, is encrypted transmissions which is opposed by constitutional watchdogs.

The police, ever trying to stay one step ahead of crime, also take advantage of emerging communications technology like smart phones, GPS, and live video. Above all, voice communication is still the preferred way for police to communicate with each other. They may not say "Calling all cars!" anymore, but there's bound to be at least one dispatcher asking, "Car 54, where are you?"

Articles about police communications, both past and future.

The evolution of police communications and what's ahead

The history of police communications

A fascinating article from 1942 about the state of police communications and some bold and accurate predictions

The prohibition origins of police radio

How police officers communicated before mobile phones

Replacing legacy police technology with smart devices

History of the LAPD's communications department

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