Passive Alcohol Sensors

Definition: Passive alcohol sensors (PAS) are small electronic devices, usually built into police flashlights or clipboards that can detect alcohol in the ambient air of a vehicle. The sensors are quick, objective, and provide another source of detection to the officer which may aid in the identification of impaired drivers.

Executive Summary: PAS devices do not require “active” cooperation by the suspect because an officer needs only to place the device within several feet of the inside of the vehicle to obtain a reading. The results from the PAS lack the precision or accuracy of a traditional breathalyzer but serve well as another means for an officer to detect the presence of alcohol much like blood-shot eyes, slurred speech or other known personal indicators. These methods of primary alcohol detection provide reasonable suspicion to alert the officer to investigate further.

More Detail: PAS provide an officer with a range of alcohol in the air of the vehicle, acting much like an electronic nose. Whereas a human nose can be deceived by other smells (perfume, gasoline, body odor); the electronic nature of the PAS can be more accurate. Research has shown passive alcohol sensors to be effective in identifying persons with BACs of 0.08 and greater with detection rates of 70% or higher.

The goal of these passive sensors is merely to aid an officer in the detection of alcohol during a stop, not to replace other more reliable and effective testing methods. This equipment helps provide law enforcement with tools to develop initial suspicion of someone breaking the law (IIHS, 1993). Because they lack the precision of other tests and can detect alcohol from sources other than the suspected impaired driver, PAS results generally are not accepted as prima facie evidence during the prosecution’s case. However, in at least one state PAS results have been admitted, not for the purpose of ascertaining alcohol concentration but, rather as one of several field sobriety tests as an indicator of intoxication. See Fernandez v. State 915 S.W.2d 572, 576 (Tex. App.-San Antonio, 1996).

Enhanced training is required for the effective use of the PAS device since these devices may be a new technology to law enforcement. Additionally, prosecutors and judges also benefit from familiarization themselves with this technology. However such training would not require great amounts of administrative resources, given the simple design of most PAS devices.

Passive alcohol sensors, are also used to detect commercial drivers with illegal BAC levels (0.04 BAC) and underage drivers with low BACs to enforce “Zero Tolerance” laws. Research has shown that passive alcohol sensors appear to be a cost-effective tool since police resources and related expenses are oftentimes a concern. Better ways to promote their use should be developed and barriers to their use ought to be overcome.

States may differ in their laws regarding passive alcohol sensors so it is best for law enforcement to review the state statute or consult with the prosecutor since not all states accept this device as a reliable indicator of DUI, especially if such evidence forms the basis or main component of what led the officer to make an arrest. Some states may require certain preconditions be met and proven for evidence from PAS to be admitted. For example, in order to be admissible, such evidence might have to be cumulative rather than determinative. An officer who provides such test results may first need to be qualified as having received training in the use of the PAC device. Proof that the device was working properly and that its continuing accuracy is routinely tested may be required.


Suggested Audience: Enforcement, Judges


Works Cited:

  • Insurance Institute of Highway Safety – Passive Alcohol Sensors Annotated Bibliography of Scientific Research, 1993.

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