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How Does A Breath Alcohol Test (Breathalyzer) Work?

Types of Breath Alcohol Tester Technologies

What Factors Are Important When Selecting a Breath Alcohol Tester?

Breath Test Evidence


A breathalyzer (or breathalyser) is a device for estimating blood alcohol content (BAC) from a breath sample. "Breathalyzer" is the brand name of a series of models made by one manufacturer of these instruments (originally Smith and Wesson, later it was sold to National Draeger), but has become a genericized trademark for all such instruments. Intoxilyzer, Intoximeter, AlcoHAWK, Alcotest, Alcosensor and Datamaster are the other most common brand names in use today. The U.S. Government's National Highway Traffic Safety Administration maintains a "Conforming Products List" of breath alcohol devices approved for law enforcement use [1].

View the DOT/NHTSA's list of approved breath alcohol screeners

View the DOT/NHTSA's list of approved evidential breath alcohol testers


Though technologies for detecting alcohol vary, it's widely accepted that Dr. Robert Borkenstein (1912-2002), a captain with the Indiana State Police and later a professor of Indiana University at Bloomington, is regarded as the first to create a device that measures a subject's blood alcohol level based on a breath sample. In 1954, Borkenstein invented his breathalyzer, which used chemical oxidation and photometry to determine alcohol concentration. Subsequent breathalyzers have converted primarily to infrared spectroscopy. The invention of the breathalyzer provided law enforcement with a non-invasive test providing immediate results to determine an individual's BAC at the time of testing. It does not, however, determine an individual's level of intoxication, as this varies by a subject's individual alcohol tolerance [2]. And the BAC test result itself can vary between individals consuming identical amounts of alcohol due to race, gender, weight, genetic pre-disposition, metabolic rate, etc. Further, the assumption that the test subject's partition ratio will be average -- that there will be 2100 parts in the blood for every part in the breath -- means that accurate analysis of a given individual's blood alcohol by measuring breath alcohol is difficult, as the ratio varies considerably.

How Does a Breath Alcohol Tester (Breathalyzer) Work?

When alcohol absorbs into your blood stream, it becomes possible to determine an individual's degree of intoxication by ascertaining the alcohol concentration percentage in the person's blood -- known as "blood alcohol concentration" ("BAC"). An individual's BAC can be measured two ways: (1) invasively (drawing a blood sample), and (2) non-invasively (breath, salvia, or urine samples). Invasive testing is generally performed at health care institutions by specialists equipped to perform the procedure, while non-invasive testing is used primarily by law enforcement officials because it is more feasible to perform. Of the different types of non-invasive testing, breath testing is the most common procedure because it is quick and less expensive.

Many people wonder how breath alcohol content (“BrAc”) is converted into BAC. As air moves in and out through the same set of respiratory tubes, continuous mixing of inhaled and exhaled air occurs. Air moves from the nose/mouth to the trachea to two tubes (one for each lung), known as the bronchi. The bronchi separate into several subdivisions, which end in a large number of tubules. At the end of the tubules are the alveoli, and a person's lung contains million of alveoli. Surrounding the alveoli is a fine network of capillary blood vessels. At this level the blood exchanges chemicals with the air in the lungs. Studies show that the alcohol concentration in the lower portion of the lungs is proportionate to the concentration of alcohol in the blood at a ratio of 2100:1.

To obtain an accurate correlation between blood and breath alcohol levels (typically 2100:1), the alcohol tester must be able to capture an air sample from the lower portion of the lungs. A person's vital capacity (volume of air that can be expelled without collapsing the lung) can range from 1 liter to 7 liters, depending on factors such as age, gender, physical condition, and disease status. If an alcohol tester requires too long of a breath sample before testing the person’s breath alcohol content, then the risk is that the person will not be able to provide a sufficient breath sample. On the other hand, if the alcohol tester captures a person’s breath alcohol content only after the person exhales a minimum amount of air, then the correlation between breath alcohol content and BAC will be poor. Typically, alcohol tester protocols will require the test subject to exhale air for at least 5 seconds to obtain a high correlation between BrAc and BAC.

Newer and more advanced alcohol testers can track the force of the exhale over time to ensure an adequate lung volume is achieved. Most professional-grade alcohol testers measure the force of the breath sample to prevent “fake blowing” through the device and inaccurate results.

Types of Alcohol Tester Technologies

There are essentially four types of technologies to measure the air in lungs to individual's estimate BAC:

  • Semiconductor Sensor Models
  • Fuel-Cell Sensor Models
  • Infrared (IR) Spectroscopy Models
  • Gas Chromatography Mode

Semiconductor Sensor Models

The presence of semiconductor units has increased rapidly over the past few years. The main advantage with semiconductor units is that they are relatively inexpensive. Since many semiconductor models are available, it is important to look at several relevant factors when selecting which unit is right for you. Based on the various factors to consider when selecting an alcohol tester, Q3 Innovations breaks down semiconductor models into two categories: Novelty Grade and Professional Grade.

  • Novelty-Grade Semiconductor Models

    Many alcohol testers in the market are designed to test passive samples of breath, which means a breath sample is taken without the use of a mouthpiece. Passive testing is common because it is easy to simply test for the presence of alcohol on the breath.  However, passive testing is typically less accurate and can often lead to unreliable results.  The results of passive testing units are greatly altered by the surrounding environment as their sensor is highly exposed to any pollutants in the air.  It is can also be difficult for the user to judge the correct distance to the space where to exhale into the unit and how hard to blow at the sensor of the unit. These units are often purchased as a unique gift or for entertainment purposes only

  • Professional-Grade Semiconductor Models

    Professional grade units meet the strict requirements for pre-market notification (510k) by the Food and Drug Administration (FDA),and model specifications set forth by the Department of Transportation (DOT)/National Highway Traffic Safety Administration (NHTSA). These units have a well-designed breath capture system and are programmed to test deep-lung air samples. The units are typically used for no tolerance testing situations such as Alcohol Abuse Clinics, Millar, Corrections, Schools, Parents, and Probation Officers. Q3 Innovations has a full series of AlcoHAWK® breath alcohol testers that are ideal for zero tolerance screening.

Fuel Cell Models

Fuel Cell units are the gold standard of handheld alcohol testers.  They are used by police officers, employers, substance abuse counselors and the like.  Professional-grade semi-conductor units and fuel cell units have similar accuracy at the calibration points, but the fuel cell units are designed to be more specific towards alcohol detection and they often have better linear accuracy away from the calibration point.  As a result, fuel cell units reduce the risk of false positive readings from non-alcohol substances.  Some of these units, such as the Phoenix 6.0 are designed for evidential testing, which means the results can potentially be used as evidence in a court of law.  The only major drawback with fuel cell units is the cost, with pricing from $400 - $1500 per unit. These models are most commonly used for workplace and law enforcement testing and screening. Lifeloc offers a full line of fuel cell models as well as training on this equipment.

Infrared (IR) Spectroscopy and Gas Chromatography Models

These units are utilized at police stations and are used mainly as evidential testers because they are extremely accurate and specific. These units are not yet manufactured to be handheld / portable units. These units are also very expensive, usually over $1000.

What Factors Are Important When Selecting a Breath Alcohol Tester?

Many factors should be considered when selecting an alcohol tester. First and foremost, accuracy should be an important factor unless you are merely looking to purchase a novelty item at a low cost. If you care about accuracy, then it is important to compare the accuracy levels listed in the specifications for each unit. However, keep in mind that the accuracy reported in the specifications is often mistakenly viewed as the true accuracy of the unit when testing a human subject. The accuracies listed in the product specifications for each unit are usually based on a controlled testing environment using an alcohol simulator device. This does not account for the ability of the alcohol tester to capture an accurate breath sample. As a result, you should consider the following factors to determine the "true accuracy" of an alcohol tester:

1) Whether the alcohol tester has passed 510(k) premarketing notification from the Food and Drug Administration (FDA) and meets the model specifications of the Department of Transportation (DOT)/ National Highway Traffic Safety Administration (NHTSA).

The Food & Drug Administration (FDA) classifies breath alcohol testers as a Class I Medical Device, which means the FDA must review and clear any breath alcohol tester to determine if it is safe and effective prior to the device being sold over-the-counter for personal use. It is a violation of federal law for a company to sell or distribute a breath alcohol detector for personal use if the device is lacking or pending FDA 510(k) clearance. Click here to view a list of the devices that have FDA 510(k) pre-market clearance for sale.

The National Highway Traffic Safety Administration (NHTSA), a division of the U.S. Department of Transportation (DOT), is responsible for testing breath alcohol testers to ensure the devices conform to the model specifications and accuracy requirements for use by law enforcement professionals throughout the USA. Click here to view the DOT/NHTSA's list of devices that meet model specifications of breath alcohol screeners.

2)  Whether the alcohol tester captures a deep lung air sample and monitors pressure.
The best alcohol testers are capable of detecting both the duration and force of an exhale. Most individuals can easily blow a steady breath for at least four seconds. Confirming the force of the exhale is important when testing another individual because older devices that only capture breath samples after a specific period of time give the test subject the ability to exhale hard enough to activate the unit but then weaken their exhale in an attempt to provide a diluted sample.

3) Whether the alcohol tester requires mouthpieces to minimize the impact of external air.
We strongly recommend alcohol testers that require the use of a mouthpiece when capturing a breath sample. Any alcohol testers that do not require the use of a mouthpiece (known as Passive Testing Units) allow other air to mix with your breath sample, which can greatly alter the accuracy of the alcohol testers.

4) Whether the alcohol tester has good sensor accuracy in a controlled environment.
We recommend alcohol testers that have a sensor accuracy of at least +/- 0.01% at the calibration point  in a controlled environment. For example, if a unit is calibrated with a solution of 0.02%, this means that testing with a 0.02% simulated breath solution would not provide readings on the unit any higher than 0.03% and no lower than 0.01%.

5) Whether the alcohol tester can be recalibrated.
Over time, all alcohol testers will need to be recalibrated. Calibration is a process where you program the internal software so that it can gauge specific BAC levels. If the sensor becomes saturated, then the results can become skewed. This is because the unit was originally calibrated when the sensor was unsaturated. This process is sort of like winding a clock. When the clock is first set it displays accurate time. However, over time the clock gradually drifts a few minutes, and eventually can be off by quite a bit if you do not occasionally reset the clock. When selecting an alcohol tester, it is imperative to select a unit that is capable of being calibrated. It is also important to know that replaceable sensor modules need to be recalibrated or replaced reoutinely.

Breath Test Evidence

The breath alcohol reading is used in criminal prosecutions in two ways. Unless the suspect refuses to submit to chemical testing, he will be charged with a violation of the illegal per se law: it is a misdemeanor throughout the United States to drive a vehicle with a BAC of .08% or higher (.02% in most states for drivers under 21). The breathalyzer reading will be offered as evidence of that crime, although the issue is what the BAC was at the time of driving rather than at the time of the test. The suspect will also be charged with driving under the influence of alcohol (sometimes referred to as driving or operating while intoxicated). While BAC tests are not necessary to prove a defendant was under the influence, laws in most states require the jury to presume that he was under the influence if his BAC was over .08% when driving. This is a rebuttable presumption, however: the jury can disregard the test if they find it unreliable or if other evidence establishes a reasonable doubt. If a defendant refused to take a breathalyzer test, most states allow evidence of that fact to be introduced; in many states, the jury is instructed that they can draw a permissible inference of "consciousness of guilt". In drunk driving cases in Massachusetts and Delaware, if the defendant refuses the breathalyzer there can be no mention of the test during the trial.

Some states don't permit data or "readings" from hand-held PBTs to be presented as evidence in court. They are generally admissible, if at all, only to show the presence of alcohol or as a pass-fail field sobriety test to help determine probable cause to arrest. South Dakota does not permit data from any type or size breath tester but relies entirely on blood tests to ensure accuracy.


Breathalyzer, http://en.wikipedia.org/wiki/Breathalyzer (last visited November 4, 2009)

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