Emergency service response codes
The emergency services in various countries use systems of response codes to categorize their responses to reported events. One of the best known is the Code 3 Response, which is used in several countries, particularly the United States, to describe a mode of response for an emergency vehicle responding to a call. It is commonly used to mean "use lights and siren."
Use of "Code 3"
Although the exact origin of Code 3 is not clearly known, its use has spread across the United States and into parts of Canada.
Code 3 was the title to a 1950s television police procedural intended to compete with Dragnet.
The Greaseman used the term in one of his songs, "I Love To Go Code 3".
Response codes
The most commonly used response codes are:
CODE 1: Non-emergency response. No lights or siren, following the flow of traffic.
CODE 2: Semi-life-threatening emergency response. Follow traffic laws, but expedite response.
CODE 3: Life-threat response. Emergency traffic, or simultaneous use of lights and siren required in order to achieve a rapid response. This allows the responding unit to ignore jurisdictional traffic laws, but does not allow the responding unit to operate without due regard to safety.