Growing up my parents used to listen to the police scanner all the time. I thought it was the dumbest thing on the planet. Every night now I turn on the scanner and listen for a few hours. Anybody else listen to a police scanner? I've found out more about people in my hometown from that than I've ever wanted to know.
Some of the guys I work with are reserve police officers and they have police radios they carry with them. Some of the stuff I hear on their radios scares the shit out of me. Kidnappings, shootings, home invasions, and gang activity. You don't want to know. It's why my wife made us get our concealed weapons permit and carry a gun to Walmart.
I have a couple family members who are cops. I know the most common ones. In the app there is a list of them, but they don't always translate to the county or city that's using them.
My wife is a dispatcher, she knows all of them. When she tells me about her day, she uses all these codes and I just nod my head like I know what she's talking about.
Download an app on your phone, Dooz, that's the easiest, as you can just search by city, municipality, department, etc. It was really cool listening to the Cambridge Police radio during the Boston Bomber search.
They can be different depending on location. Basic ones are pretty standard, but there can be some variances. Common ones (besides 10-4 etc) from my firefighting days were: 10-1 bad reception/broadcast 10-2 good reception/broadcast 10-6 busy/on a call 10-7 out of service/off duty 10-8 in service/on duty/ often preceded by 10-98 10-45 accident no injuries 10-46 accident with injuries 10-27 & 28 license/registration check 10-10 pretty much eating dinner 10-59 fight 10-72 fire 10-82 request backup 10-97 arrived on scene 10-98 finished call There's a ton of them.