Ignition interlock technology based on breath alcohol test devices for detecting and preventing alcohol impaired driving does appear feasible at this time. Devices that measure a driver's breath alcohol concentration (BAC) level are currently being marketed and used. Laboratory tests have shown the current breath test ignition interlock devices to be relatively accurate in detecting low driver BAC levels. These devices contain anti-tampering and circumvention measures that appear to reduce the likelihood of many forms of tampering and circumvention. Current interest has focused on applying this technology to convicted DWI offenders as a condition of probation or to obtain a restricted driving privilege. Critical information necessary to estimate the potential effectiveness of these devices in this application, such as evidence that the devices function properly under real-world conditions, is lacking. There is not yet enough evidence available to judge how effective these devices will be in deterring alcohol impaired driving and related crashes.