• Top Lawyers - San Diego Magazine
  • Former Deputy San Diego City Attorney
  • Former USMC Captain
  • Located Directly Across From Vista Courthouse
  • Over 150 Five Star Reviews on Google and Yelp

Attorneys William R. Christoph & Nicholas W. Christoph

Study finds many personal breathalyzers are inaccurate

On Behalf of | May 18, 2021

It’s not an uncommon sight at San Diego nightclubs and bars: as a group of friends prepares to leave, one or more of them will pull out personal alcohol breath-testing devices (often referred to as breathalyzers). People will blow into the handheld devices that pair with smartphones and get a blood alcohol concentration (BAC) reading within seconds.

Personal breathalyzer owners know that if they’re pulled over when they’re driving home, they may be arrested for driving under the influence (DUI) depending on their BAC.  So they’ll often perform a test at the bar or club to ensure that they’re below the legal BAC threshold before getting behind the wheel.  It is unlawful to drive with a BAC of .08 or more and it is also unlawful to drive while “under the influence of alcohol” even at a lower BAC.   You are presumed to not be under the influence below .05 BAC, and are presumed to be under the influence .08 or more BAC.  However, you could still be charged with a DUI even at levels .05 to .08 BAC as there is evidence of impairment at those levels.  Additionally, your blood alcohol level continues to rise for a period of time after the last drink so your test before driving may not be accurate as that last drink continues to be absorbed in your bloodstream.  .

Missing the mark

Unfortunately, the personal alcohol breath-testing devices are not always accurate. According to new research, people who rely on the devices to stay clear of a DUI might find themselves facing the very charge they had hoped to avoid.

Researchers at the Perelman School of Medicine at the University of Pennsylvania conducted a study of personal breathalyzers published recently in a scientific journal. They compared the accuracy of six personal testing devices against a police-grade breath-testing device and against a blood test to determine BAC levels.

Exceeding the threshold

Researchers enlisted the help of 20 moderate drinkers between 21 and 39 years old. They were each given three doses of 100-proof vodka over 1 hour and 10 minutes. The goal was to exceed the legal threshold with a BAC of .10 percent.

After each serving of vodka, the BAC of each participant was measured with both the personal breathalyzers (Alchohoot AHT 101, BACtrack Mobile Pro, and DRIVESAFE Evoc, BACtrack Vio, Drinkmate, and Floome.) and the police-grade device (Intoxilyzer 240).

After the three servings were consumed, the blood test was performed in addition to tests with the half-dozen personal devices and the Intoxilyzer.

Data dive

Researchers found that all seven testing devices underestimated BAC levels by more than .01 percent.

Two devices – the Drinkmate and Evoc – failed more than half the time to detect when a person’s BAC had reached the legal threshold. That means that a driver with a BAC of .08 percent would be told by those breathalyzers that it’s OK to drive – but they’d face arrest if tested by a police officer.

The two devices that measured closest to the Intoxilyzer were the BACtrack Vio and Alcohoot.

Skewed results

Let’s not forget, however, that the police-grade Intoxilyzer was itself shown to be inaccurate in this study. And in a New York Times investigation two years ago, the newspaper issued a scathing assessment of alcohol breath-testing devices used by law enforcement agencies across the nation. The devices “generate skewed results with alarming frequency, even though they are marketed as precise to the third decimal place,” the Times reported.

The newspaper found that improperly calibrated testing devices would generate “results that were at times 40 percent too high.”

If you’ve been charged with driving under the influence of alcohol, discuss with an attorney the details of alcohol testing, roadside sobriety tests and your arrest.



Google 5 Star Reviews

Over 150 Five Star Google and Yelp Reviews

5 stars
Yelp 5 Stars Logo


I highly recommend Christoph Law Offices to everyone. Nick is a true professional who will go above and beyond for his clients. Thank you!
– Mahir B.


Amazing attorneys! Bill Christoph was very helpful during my case. He was always quick to get back to me about my questions.
– Collin W.


Great experience overall having William Christoph as my attorney. He understands his client, very insightful and is an expert in his field.
– Soheila N.

Defending Against DUI and Criminal Charges Throughout San Diego County

TOP RATED In The Legal Community
Martindale-Hubbell AV Preeminent Rating, Peer Rated for Highest Level of Professional Excellence
AVVO Rating 10 Superb Top Criminal Defense