The alcohol interlock is a sophisticated device that requires a driver to provide a breath sample that is tested for alcohol before the vehicle can be started.

It also requires the driver to provide repeated breath tests while the vehicle is in use to ensure the driver remains sober. These devices require about 45 minutes to install and the installation should be completed by a licensed, professional installer.

The device uses a semiconductor or electrochemical (fuel cell) sensor to detect and measure alcohol concentrations in breath samples. The most commonly used sensor in modern alcohol interlock devices is the fuel cell sensor due to its alcohol detection specificity and less frequent servicing requirements in comparison to semiconductor ignition interlocks. Electrochemical ignition interlocks are highly accurate in detecting alcohol. The operation of these devices is governed by NHTSA model specifications which are a guideline that these devices must meet in order to be approved for use. These specifications are currently being revised and updated. Many states have also established a certification process for interlock devices.

Alcohol interlocks with fuel cell sensors are reliable and accurate, even under extreme weather conditions, pressure, and elevation; although in some instances a longer warm-up time may be required. These devices possess a variety of programmable features that are frequently required by individual jurisdictions. In many instances, devices are programmed by the manufacturer and certified by a state agency to ensure they meet the requirements and/or specifications of the jurisdiction. In some instances, features may be programmed by service providers. In these instances, monitoring of service providers through vendor oversight protocols by the state is recommended to reduce opportunities for incorrectly programmed devices.

Several programmable features are available on most alcohol interlock devices. These include language and visual display, BrAC threshold, breath volume, lock-out time, stall protection time, pull-over notice, recall notice, and other emerging features such as GPS and real-time reporting. Modern alcohol interlocks are also equipped with mandatory anti-circumvention features as mandated by government guidelines (NHTSA 1992) which include sealed wiring, connectors, temperature and pressure gauges, driver recognition systems, and data recorder component. Related to the anti-circumvention features is the running re-test, a procedure which requires a driver to provide continued random, repeated breath tests once the vehicle has been successfully started. The purpose of the running re-test is to prevent the driver from drinking once the vehicle has started and is left idling and also to detect escalating BrAC levels in the driver once the vehicle is in motion. The emergency override is another feature that may be available on some alcohol interlocks if permitted by the jurisdiction. It allows the driver to override the system one time only in the event of an emergency; however, some concerns have been expressed regarding the potential for this feature to allow an intoxicated individual to operate a vehicle and the liability that this may create.

In addition to current features, various types of alcohol interlock technology are being considered for future use with the intention that these devices themselves may be installed as a standard feature on all newly manufactured vehicles. In order to ensure compliance and public acceptance of these proposed features, the devices must be small, fast, accurate, and reliable and cannot impede or interfere with starting the vehicle if the driver is not alcohol impaired. These potential future technologies include infrared spectroscopy and vehicle-based impairment detection. While technological advances are being made, it is unlikely that alcohol interlocks as a standard device on all vehicles will occur during the next decade.

Last updated December 2021