Passive Alcohol Sensors

Passive alcohol sensors (PAS) — so called because they do not require active cooperation by the person being tested — are usually integrated into police flashlights or clipboards (for daytime use). These devices sense alcohol in the exhaled breath near the driver’s mouth. They are more objective and reliable than an officer’s nose, and they have been found to significantly improve the detection of drunk drivers. Proper training is required for effective use.

Unlike PBTs, they are not intrusive and are unlikely to be challenged based upon constitutional prohibitions against unreasonable search and seizure. Passive alcohol sensors can be particularly helpful in reducing the number of hardcore drunk drivers who go undetected at checkpoints.

While PAS results are usually not permitted in the court as prima facie evidence of DWI, they can establish probable cause for further investigation by an officer

Studies have found these devices to be very effective. Their use has led to fewer high BAC drivers avoiding arrest and fewer low or zero BAC drivers being detained. A series of studies has shown passive sensors increase by about 50 percent the detection rate of drivers with BACs at .10 or greater in checkpoint operations (Voas et al. 1997).

One study found passive sensors can identify about 75 percent of drivers with BACs at or above .10 and 70 percent of BACs at or above .08 — a vast improvement of the 40 to 50 percent detection rate by police officers at checkpoints not using sensors (Farmer et al. 1999).

Burns, M.M. 1999. Identification of alcohol impairment outside the vehicle: Field sobriety tests. Issues and Methods in the Detection of Alcohol and Other Drugs. Washington, DC: Transportation Research Board, National Research Council.

Farmer, C.M., Wells, J.K., Voas, R.B., and Ferguson, S.A. 1999. Field evaluation of the PAS III Passive Alcohol Sensor. Journal of Crash Prevention and Injury Control 1(1): 55–61.

Fell, J.C. 2000. Comments on “Increasing the Opportunities to Examine Impaired Drivers.” Issues and Methods in the Detection of Alcohol and Other Drugs. Washington, DC: Transportation Research Board, National Research Council.

Grey, S.L. Spring 2001. Passive alcohol sensors and the fourth amendment. Impaired Driving Update. Kingston, NJ: Civic Research Institute, Inc.

Hedlund, J.H. 2000. What’s needed to improve police detection of alcohol and other drugs in drivers. Issues and Methods in the Detection of Alcohol and Other Drugs. Washington, DC: Transportation Research Board, National Research Council.