Ten-codes are a means of communication between law enforcement officers using numeric codes for frequently used phrases, says About.com. They originated in the United States around 1920 to 1930.
A man named Charles Hopper is credited with the establishment of the first set of codes, according to About.com. The Association of Public Safety Communications Officials published the first official set in 1940. In 1947 this organization expanded the codes and made them more concise and standardized, says eInvestigator.com. The codes serve two purposes: to reduce speech, thus leaving airwaves available, and to keep officers safe. By keeping radio communication to a minimum, officers are better able to focus on whatever situation they may be facing.
While the codes were intended to be standardized, different meanings have sprung up making communications between jurisdictions somewhat difficult, though there are some common codes. A 10-4 is an affirmative or O.K. and a 10-20 can mean an officer location check, as stated by About.com. In 2005, however, a massive push by FEMA and the Department of Homeland Security began to use plain English when using radio communications, states eInvestigator.com. The thinking behind this is that since there is no universal standard, communications are easier if plain English is used.