Accuracy of Breathalyzers a Threat to Law-Abiding Drivers

About half of all alcohol-related traffic crash deaths involve drivers with BACs of at least 0.16 or higher. (BAC is alcohol breath concentration.) That’s twice the legal limit. Many of these high-BAC drivers are hard core drunk drivers. They repeatedly abuse alcohol and drive while drunk. Hard core drunk drivers are a major threat to the safety of themselves and others. Breath analyzers are a major tool in convicting such dangerous offenders. So the accuracy of breathalyzers is important. Without it,the guilty can go free. And the innocent can end up with a conviction.


I.   Accuracy of Breathalyzers

II.  Solutions to Breathalyzer          Inaccuracy

III. Resources

Breath analyzers have various brand names. Breathalyzer, Intoxilyzer, Alcosensor, Alcoscan and BAC Datamaster are examples. These don’t actually test BAC. That requires the analysis of a blood sample. Instead, they estimate BAC indirectly.

I. Accuracy of Breathalyzers

Different types of machine use different techniques. Larger machines tend to yield better estimates than hand-held models. That’s why some states don’t permit estimates from hand-held machines in court. South Dakota does not even permit evidence from any type or size breath tester. It uses blood tests to ensure accuracy and protect the innocent.

A major problem with some machines is simple. They identify the ethanol found in alcohol beverages. No problem there.  But they also identify other substances similar in molecular structure. That’s any compound containing the methyl group structure. Over  100 compounds are in the human breath at any one time.  And 70 to 80 percent of them contain methyl group structure. Machines can incorrectly report them as ethyl alcohol. The more different ethyl group substances the machine detects, the higher will be the false BAC estimate.


Dieters and diabetics can have acetone levels hundreds and even thousand of times higher than that in others. Some breath machines can falsely report acetone and many other substances as alcohol.

One investigator reported that alcohol-free subjects can generate BAC readings of about .05 after eating various types of bread products.

accuracy of breathalyzersSubstances in the environment can also lead to false BAC readings. For example, an alcohol-free subject applied a pint of contact cement to a piece of plywood. He then applied a gallon of oil-base paint to a wall. The total activity lasted about an hour. Twenty minutes later the subject blew into an Intoxilyzer. It registered a BAC of 0.12. That’s 50% above the legal limit

Similarly, a painter with a protective mask spray painted a room for 20 minutes. Although a blood test showed no alcohol, an Intoxilyzer falsely reported his BAC as .075.

Any number of other products found in the environment can cause erroneous BAC results. These include compounds found in lacquers, paint removers, celluloid, gasoline, and cleaning fluids.

Other common things that can reduce the accuracy of breathalyzers  are alcohol, and blood or vomit in the mouth. Also electrical interference from cell phones and police radios, tobacco smoke, dirt, and moisture.


Breath testers can be very sensitive to temperature and will give false reasings if not adjusted for air temperatures. The temperature of the subject is also very important. Each one degree of body temperature above normal will cause a substantial elevation (about 8%) in apparent BAC.

Many testers asume a 2,100-to-1 ratio in converting alcohol in the breath to estimates of alcohol in the blood. However, this ratio varies from 1,900 to 2,400 among people. It also within a person over time. This variation will lead to false BAC readings.

Physical activity and hyperventilation can lower apparent BAC levels. One study found that the BAC readings of subjects decreased 11 to 14% after running up one flight of stairs. They decreased and 22-25% after doing so twice. Another study found a 15% decrease in BAC readings after vigorous exercise.


Some breath analysis machines assume a hematocrit (cell volume of blood) of 47%. However, hematocrit values range from 42 to 52% in men and from 37 to 47% in women. A person with a lower hematocrit will have a falsely high BAC reading.

Failure of officers to use the devices properly is a source of error. So is failure to have the machines properly maintained and re-calibrated as required.

Research shows that breath tests vary at least 15% from actual blood alcohol concentration. At least 23% of all individuals tested will have a BAC reading higher than their actual BAC. That’s about one of every four.

One writer has made this observation.

Breath testing, as currently used, is a very inaccurate method for measuring BAC. Even if the breath testing instrument is working perfectly, physiological variables prevent early reasonable accuracy…. Breath testing for alcohol using a single test instrument, should not be used for scientific, medical or legal purposes where accuracy is important.1

II. Solutions to Breathalyzer Inaccuracy

There are good ways to virtually eliminate an unfairly conviction for DUI or DWI. One is to choose not to drink. Another is to pace the rate of drinking and follow other tips for maintaining a low BAC. A third is to have a designated driver. If you use a designated driver, you never have to worry about the accuracy of breathalyzers.

1. Don’t Drink

If you choose not to drink, you’ll find that it’s not a big deal to decline a drink. Here are some possibilities.

  • No thanks.
  • No thanks; I feel good enough already.
  • Sorry, my analyst won’t let me.
  • I can’t because I get high on grape juice.
  • Not now — I’m testing my willpower.
  • No thanks — I want a clear head to appreciate you fully.
  • Not right now — the party’s wild enough as it is.
  • Sorry, I never drink on Friday (or whatever day it is).
  • Sorry, I promised my parents (spouse, date, etc.) that I wouldn’t.
  • No thanks — I prefer to watch.
  • No thanks — Suzie (or whoever) can’t stand me when I drink.
  • Sorry — I’m taking medication.
  • No thanks, but I’d love to have a Pepsi.
  • Sorry, but I’m serving as designated driver.

You can also “lose” alcohol drinks. Or order water, orange juice, seltzer with a twist of lemon, or  another beverages that lool like an alcohol  beverages. Most people don’t really pay much attention to how much others are drinking. You might find that you actually enjoy yourself as much or more without becoming intoxicated. There’s no hangover and it’s certainly much safer.

2. Keep Your BAC Low

If you choose to drink you can keep your BAC low.  Here are some tips.

  • The typical can of beer, glass of dinner wine, or shot of spirits has the same amount of pure alcohol. A breathalyzer can’t tell them apart.
  • A general rule of thumb is to have no more than one drink per hour.
  • Eat or munch while drinking. This helps keep BAC low.
  • Sip your drinks.
  • Don’t play any drinking games or contests.
  • Have non-alcohol drinks betwen alcoholic ones.
  • Be careful when drinking punches or drinks in unusual size containers. That’s because its’s hard to know how much alcohol they contain. Thus, it’s hard to pace them.

3. Use or Serve as a Designated Driver

Consider either using or serving a designated driver. A designated driver agrees to drink no alcohol and drive others home. The others are free to drink or not as they choose. Many bars provide free non-alcohol beverages to designated drivers.

Designated drivers have probably saved 50,000 lives and spared many more thousands of people from suffering injury from druink driving.2 Over nine out of 10 Americans who attend social evernts would like to see more designated drivers.3 And the proportion of people either using or serving as a designated driver has increased dramatically over time. Over 73,000,000 Americans either served as or benefitted from a designated driver.4

A designated driver helps others

  • Avoid embarrassment.
  • Keep their driver’s licenses.
  • Avoid fines.
  • Stay out of jail.
  • Prevent needless injury and death.5

The designated driver non-drinker has a respected role at social functions. There is no pressure to drink. Serving as designated driver can also help legitimate a personal choice not to drink.6

Tips for designated driving.
  • Identify the designated driver ahead of time.
  • Consider taking turns serving as designated driver. Look after your friends and family and they can look after you.
  • Larger groups should have more than one designated driver.7

Don’t Worry about the Accuracy of Breathalyzers.

Breathalyzers may be inaccurate and lead to unjust fines, imprisonment and other serious problems.  But you needn’t worry about the accuracy of breathalyzers.  Simply choose not to drink. To drink but keep a low BAC. Or have a designated driver.

III. Resources

Popular Books Relevant to Accuracy of Breathalyzers

Brezina, C. Alcohol and Drug Offenses. Your Legal Rights. NY: Rosen, 2015.

Dasgupta, A. Beating Drug Tests and Defending Positive Results. Humana, 2010.

Goodman, K. and Simon, K. Safe Road Home. Stop Your Teen from Drinking & Driving. NY: Sterling, 2005.

Head, B. and Joye, R. 101 Ways to Avoid a Drunk Driving Conviction. Atlanta: Maximar, 1991.

Hudson, T. The Drinker’s Guide to Driving. The Secrets of DUI, From One of America’s Top DUI Lawyers. BookBaby, 2013.

Keech, C. and Fairchild, C. Dude, What are My Rights? The Self-Help Legal Survival Guide Ages 18-25. Kansas City, MO: Keechild, 2004.

Technical readings on Accuracy of Breathalyzers

Joseph, J. Are Breath Tests Accurate? Defense Lawyers Often Challenge Their use as Evidence, and Win. Also

Peach, R. Who tests the DUI test? Defense can’t. New Jersey won’t let lawyers inspect new breath tests. Nat Law J, 2000, 23(6), A4.

Smith, J.S., and Nesci, J. North Carolina DWI Defense. Tucson: Lawyers & Judges, 2016.

Taylor, L. Drunk Driving Defense. NY: Aspen Law, 2000. (Updated continually with supplements.) Best single source on accuracy of breathalyzers.

1. Hlastula, M. Physiological errors associated with alcohol breath tests . The Champion, 1985, 9(6). Quoted in Taylor, L. Drunk Driving Defense. NY: Aspen Law and Business, 2000.
2. AP. Designated Driver Campaigns Working. Houston Chronicle, 11-30-07, p. A14.
3. Gallup polls reported in National Commission Against Drunk Driving. A Guide to Community-Based Designated Driver Programs. (
4. Designated Driver Campaign Working, Says Inventor (
5. Project CHEERS to the Designated Driver (
6. Nat Comm Against Drunk Driv. A Guide to Community-Based Designated Driver Programs (
7. Alberta Tran & Utilities. Designated Driver – A Smart Choice. Edmonton, Alb, 1996 (