Q: A lot of people say 420 is a police radio code for marijuana. A: “All units, all units available, please respond to a 420, marijuana smoking in progress.” No. But interestingly, 420 is the radio code for homicide in both fact (the Las Vegas Police Department) and fiction (CSI).

What's a 420 in police code?

Q: A lot of people say 420 is a police radio code for marijuana. A: “All units, all units available, please respond to a 420, marijuana smoking in progress.” No. But interestingly, 420 is the radio code for homicide in both fact (the Las Vegas Police Department) and fiction (CSI).

When did 420 become a police code?

Chris Conrad, curator of the Oaksterdam Cannabis Museum in Oakland, California, says 420 started as a secret code among a group of friends at San Rafael High School in the early 1970s who called themselves “the Waldos.” They would often meet at 4:20 p.m. to get high.