2.4 Passive Alcohol Sensors
A passive alcohol sensor (PAS) detects alcohol presence in the air. The sensor usually is integrated into a flashlight or clipboard. An officer holds the flashlight or clipboard near the driver’s mouth, where it measures alcohol presence in the air where the driver is breathing. The PAS displays a BrAC range, such as a red light for any BAC at or above .08 g/dL. It can be used without the driver’s knowledge and without any probable cause because the PAS is considered “an extension of the officer’s nose” and records information that is “in plain view” (Preusser, 2000).
Based on the survey conducted by Eichelberger and McCartt (2016), the majority of police agencies do not have PAS equipment. In one survey only 15% of the municipal, county, and State agencies (out of 235 total) used PAS, and with varying frequency.
Several PAS models are available commercially. They are generally reliable and effective at detecting alcohol in the surrounding ambient air. In one study, breath samples and PAS measures were obtained from over 12,000 drivers. Results showed that a PAS score was a strong predictor of a driver’s BAC status, leading to the conclusion that “the PAS can be an effective tool for officers when deciding whether to initiate a DWI investigation” (Voas et al., 2006). NHTSA does not maintain a list of PAS models.
Use: PAS units are typically used at the vehicle window after a traffic stop or at a checkpoint. A PAS report of alcohol presence may give the officer probable cause to request further examination with SFSTs or a PBT device. Except for the Eichelberger and McCartt report (2016), no other data are available on how many PAS units may be in use.
Effectiveness: The PAS is especially effective at detecting impaired drivers at checkpoints, where officers must screen drivers quickly with little or no opportunity to observe the drivers on the road. Evaluations show that officers using PAS at checkpoints can detect 50% more drivers at BACs of .10 g/dL or higher than officers not using PAS (Century Council, 2008; Farmer et al., 1999; Fell et al., 2004; Voas, 2008). The PAS appears to be especially effective in assisting officers who rarely make arrests for DWI to make more arrests. (Fell, Compton, & Voas, 2008).
Costs: PAS units cost from $300 to $700 apiece.
Time to implement: PAS units can be used as soon as they are purchased and officers are trained in their use and maintenance. Training can usually be accomplished quickly.
- Acceptance by law enforcement: Officers tend to dislike using the PAS. Common reasons given by officers are they require officers to be closer to drivers than they wish to be, they require some portion of officers’ attention at a time when they may have other things to be concerned about (including personal safety), or they may keep officers from having a hand free (Preusser, 2000; Eichelberger & McCartt, 2016). Other officers believe they can detect the odor of alcohol accurately without assistance from PAS devices (Preusser, 2000).
- Other drugs: As with a PBT, a PAS cannot detect the presence of drugs other than alcohol.