Modern microelectronics technology makes it possible to develop a nearly foolproof device that prevents an alcohol-impaired driver from starting a motor vehicle. The car ignition interlock device also provides the driver with immediate feedback on excessive blood alcohol content and; thus, is likely to result in behavior modification. Judges in five States are already using the device with drunk drivers. This has solved a dilemma for the criminal justice system: 80 percent of individuals with suspended or revoked licenses continue to drive illegally; suspension or revocation may jeopardize the job of the driver, thus increasing the likelihood of alcohol consumption. The use of the interlock device as a sanction does not depend on the availability of police for enforcement, is difficult to circumvent, can be set to a predetermined blood alcohol determination, minimizes inconvenience to the user when he or she is sober, and is capable of yielding a permanent record that can be valuable in determining the rate and extent of behavior modification that has occurred.