Past studies have demonstrated that police officers fail to detect a substantial proportion of alcohol-impaired drivers during traffic enforcement and that the use of passive alcohol sensors (PAS) could increase the driving-under-the-influence (DUI) arrest rate. Does the use of a PAS in routine traffic enforcement by officers without specialized DUI training increase the detection and arrest rate of alcohol-impaired drivers? In Anne Arundel County, Maryland, the Police Department provided the PAS devices to 24 randomly selected officers, divided equally between two squads of 12 officers each (one squad with the PAS and one squad without). After both squads made approximately 500 traffic stops each, the squads switched roles with regard to using the PAS, and the pattern was repeated. Overall, there were no significant differences in the DUI arrest rate between the officers with the PAS and the officers without the PAS, although there was evidence that the PAS helped some officers increase their DUI arrests. In summary, the PAS is probably best used at sobriety checkpoints rather than during routine stops.