Although there are no universal standards for police dispatch codes, most police departments use ten-codes, such as 10-4 meaning affirmative and 10-20 referring to the officer’s location or that of the call, according to About.com. Departments use signal codes to indicate the nature of the call.
Ten-codes were developed during the early days of police dispatch through radios. With these early radios, the electronics took time to warm after keying the microphone, cutting off the first syllable the officer spoke. Departments trained officers to key the mike, wait a second and begin their transmission with a "10" to ensure they transmitted the important message, reports About.com. Most accounts credit Charles Hopper of the Illinois State Police with developing these codes.
Signal codes include a signal four for an auto accident, signal 10 for a stolen vehicle and signal zero for an armed suspect or weapon involved in the situation, indicates About.com. In addition, California police departments often use a three-number code that refers to the section of the state statutes covering the crime. They are known as hundred-codes, with a one-eight-seven representing a murder and a four-five-nine meaning a burglary.
Police use codes to keep conversations on the radio short, according to About.com. The Federal Communications Commission requires limiting the time departments use radio communication to free up bandwidth.