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Use: High
Time: Short

Alcohol measurement devices are stationary or portable alcohol sensors used to measure a driver’s BrAC. Law enforcement officers typically use these devices in the field to help establish probable cause for a DWI arrest. The driver blows into a mouthpiece and the device displays a numerical BrAC, such as .12 g/dL.[1] Alcohol measurement devices are reliable and effective tools to aid law enforcement officers in detecting alcohol (NHTSA, 2021b).

There are two main categories of breath test devices used by law enforcement: evidential breath test devices (EBTs) and preliminary breath test devices (PBTs). PBTs, also known as screeners, are hand-held devices used at the roadside by officers in their investigation to determine if there is probable cause for an arrest. EBTs are State-approved, conform to established specifications, and can be portable or stationary. The results from EBTs can be used as evidence in court.

NHTSA conducts independent testing of devices and provides a “Conforming Products List” of alcohol screening (PBT), alcohol testing (EBT), and calibration units for these devices. Devices included on NHTSA’s Conforming Products Lists are eligible for purchase using Federal funds (NHTSA, 2021b).

Other tools for law enforcement are passive alcohol sensors (PASs). These are usually integrated into flashlights or clipboards and measure alcohol presence in the air where the drivers are breathing. They are particularly useful in situations such as checkpoints where officers need to screen drivers quickly. The breath test device displays a BrAC range, such as a red light for any BAC at or above .08 g/dL. The PAS 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). A PAS report of alcohol presence may give the officer reasonable suspicion to request further examination with SFSTs or an alcohol measurement device.

Several PAS models are available commercially. They generally are reliable and effective at detecting alcohol in the ambient air. In one study, both 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 test PAS devices.


In most States screening devices can be used in an officer’s investigation for probable cause for arrest; they are rarely used as evidence in court. One exception is California, which allows PBT results as evidence of presence of alcohol (Nesci, 2015). California officers can use PBT evidence to enforce zero-tolerance laws for drivers under 21; an officer at the roadside can issue a citation and seize the driver’s license (Ferguson et al., 2000). EBTs are commonly used to provide evidence of alcohol impairment that is presented in court.

Little data are available on how frequently PAS units are used. In a nationwide survey of law enforcement agencies, less than a quarter reported using PAS equipment to improve detection of alcohol-impaired drivers (Eichelberger & McCartt, 2016).


Law enforcement officers generally agree that breath test devices are useful. Sixty-nine percent of the 2,731 law enforcement officers surveyed by Simpson and Robertson (2001) supported greater breath test devices availability and use. Breath test devices are especially valuable for two classes of drivers who may appear to perform normally on many tasks:  drivers with high tolerance to alcohol (Simpson & Robertson, 2001) and drivers under 21 who may be in violation of zero-tolerance laws (Ferguson et al., 2000). A breath test device also can be useful at crash scenes where a driver is injured and unable to perform an SFST. There is some evidence that breath test devices use increases DWI arrests and reduces alcohol-involved fatal crashes (Century Council, 2008).

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 devices 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 (Fell, Compton, & Voas, 2008).


Breath test devices cost $200 to $2,000 a piece, with PBTs typically costing $300 to $700. Many law enforcement departments have only a limited number of breath test devices and most patrol officers do not have regular access to them. Officers surveyed by Simpson and Robertson (2001) estimated that three-fourths of all DWI arrests occur on routine patrols, so DWI detection would be substantially improved if every patrol officer had a breath test device.

Time to implement:

Breath test devices and PAS units can be used as soon as they are purchased, and officers are trained in their use and maintenance. Breath test devices instruments must also have regular calibration checks. Most law enforcement agencies have the facilities to conduct these checks.

Other considerations:

  • The “one test” rule: Some State statutes allow only one chemical BrAC/BAC test can be obtained from a driver arrested for DWI. In these cases, the State would rather the test be an evidential device rather than a screening device.
  • Other drugs: PBT, EBT, and PAS devices are designed strictly for identifying alcohol and cannot detect the presence of drugs other than alcohol.
  • Acceptance of PAS by law enforcement: Some officers reportedly dislike using the PAS. Common reasons for not using PASs are they require officers to be closer to a driver than they consider safe, and they require officers to attend to the device as well as the driver (Preusser, 2000; Eichelberger & McCartt, 2016). Other officers believe they can detect the odor of alcohol accurately without assistance from PASs (Preusser, 2000).
  • Calibrating Breath Alcohol Testing Devices: Calibration is a crucial element of any successful Alcohol Breath Testing Program to ensure the proper use, care, and accuracy of breath testing devices. Breath alcohol devices are required to have quality assurance plans that specify the inspection, maintenance, calibration requirements, and intervals of recalibration. Calibrating Units aid in this process by providing known concentrations of ethanol vapor for the calibration checks of instruments that measure breath alcohol. Owners of the devices must also maintain records of the inspection, maintenance, and calibration activities performed on the devices. Calibration is carried out by either the device’s manufacturer or a maintenance representative, certified by the manufacturer, a State health agency, or other appropriate State agency.

[1] BrACs are normally recorded in units of grams per 210 liters of breath, but are “converted” to grams per deciliter, g/dL, simply to keep the terminology standardized and equivalent to blood tests.