The purpose of an alcohol interlock is to prevent drivers from starting their vehicle if they have been drinking. The device requires the driver to blow into a breath alcohol testing device connected to the starter or other on-board computer system in order to start the vehicle, and also requires repeated breath tests while the vehicle is in use to ensure the driver continues to remain sober. While the alcohol interlock prevents the engine from starting and provides a warning if a positive breath sample is detected, the device will never shut off an engine that is already running.

Alcohol interlock devices must meet a range of technical criteria before being approved for use in a jurisdiction and require installation by a licenced installation centre. These devices possess a wide range of programmable options. Several anti-circumvention features have been incorporated into the alcohol interlock to ensure efficient functioning and minimize tampering and circumvention attempts.

More detailed information about the functioning of the alcohol interlock device and its installation, the accuracy of these devices, and the technical criteria they must meet in order to be approved for use in a jurisdiction are provided below. In addition, the impacts of mouth alcohol and various climatic conditions are discussed, and an overview of the general options and features of alcohol interlock devices is given. Finally, the types of alcohol interlock technology that are being considered for future use in all vehicles are described in more detail below. Research references are included.