If you've ever seen an American police movie, you've heard conversations like this:
Dispatcher: "Unit 3, you read?"
Patrol Officer: "10-4, base."
Dispatcher: "What's your 10-20?"
Patrol Officer: "Cedar and Pine. Uh. . . 10-23, base."
Patrol Officer: "Got a 10-42 here."
Dispatcher: "Roger that. 10-37."
And so it goes. This is called "cop talk."
It's a language all its own, though many of the so-called "ten codes," 10-8, 10-20, and so on, were borrowed from long-distance truckers. "10-4": Message received. Your "10-20" is your location. A "10-17" is serious. It means an officer has an urgent situation.
These codes began way back in the 1920s, when police had only one frequency assigned to them. You had to keep the chatter brief. "10-4" was a lot more efficient than, "Yeah, Frank, I hear ya just fine out here."
But there's bad news for those who love police jargon. Many agencies are doing away with "ten-codes" and telling their officers to use plain English. That's because some of the codes have taken on different meanings. A "10-13" means "officer in trouble" in one town. But someplace else, it's just a routine request for a tow truck. This caused serious problems when law-enforcement agencies descended upon the World Trade Center and the Pentagon en masse following the terrorist attacks of September 2001.
A lot of police officers are unhappy that the "ten codes" are being abandoned. They can't get used to talking in sentences, and "10-4s" and "10-20s" keep slipping into their calls. And they're bitter because the ten-codes give police work a touch of glamour, even though it doesn't take criminals long to figure out what they stand for.
Ten-codes are still around, but in more and more agencies, they're a "big 10-7": "out of service, leaving the air."