Category Archives: Breathalyzers
Prosecutors in the state of Massachusetts have agreed to stop using breathalyzer results dating back to 2011 as a result of improper calibration of the breathalyzers when the machines were first purchased by the state. What’s more, state officials later attempted to hide the machines’ flaw from both defense attorneys as well as prosecutors.
The agreement will be presented this week to Judge Robert Brennan, who has been overseeing the proceedings challenging the reliability of the Draeger 9510 since 2015.
Although prosecutors in Massachusetts had already agreed to stop using results from June 1, 2011 to June 14, 2014, defense attorneys learned that state officials in the Office of Alcohol Testing, which is part of the Massachusetts State Police Crime Lab, had withheld hundreds of documents that a judge had ordered them to overturn. Those documents showed a higher calibration failure rate than state officials had previously reported.
According to defense attorney, about 36,500 test results have been affected by the calibration flaw. This includes nearly every breathalyzer result obtained since 2011.
People who were convicted of a DUI where the breathalyzers results were obtained from within that timeframe can seek a new trial if their conviction was based solely on the breathalyzer results. People convicted of a DUI cannot, however, seek a new trial if their conviction was at least partly based on other evidence of intoxication such as observed poor driving by witnesses or police, video, or field sobriety tests.
According to Jake Wark, a spokesman for the Suffolk County District Attorney’s office, the actual number of affected cases will be “significantly lower” than 36,500 because it will not include cases where a breathalyzer was given to a person before being put into protective custody or where someone was given a breathalyzer to show them how the machine works.
Contrary to the usual adversarial rapport between defense attorneys and prosecutors, defense attorneys are maintaining that prosecutors and law enforcement are not to blame for the monumental blunder.
“It was not the assistant district attorneys who were withholding the material, said Joseph Bernard, an attorney leading the litigation over the machines. “They had nothing to do with this and when they found out, they rose up.”
Prosecutors are, however, still arguing to use the results in DUI cases involving death or severe injury, or in fifth or subsequent DUI cases. Additionally, prosecutors are proposing a cutoff date of August 31, 2017, after which they can begin using the breathalyzer results again.
Defense attorneys are arguing that the use of the breathalyzer results should continue to be halted until the state lab obtains accreditation by a national standards group, ANSI-ASQ National Accreditation Board, which likely wouldn’t happen until 2020.
It shouldn’t come as a surprise to anyone where I fall on this. If the results are faulty, they should not be used in any DUI case, including those that involved death or serious injury and fifth or subsequent DUI’s. The seriousness of the offense does not justify the use of tainted evidence.
Furthermore, those convicted of a DUI should not be barred from re-trial simply because other evidence existed. Just because other evidence exists that tends to show intoxication doesn’t mean that that evidence alone and without the breathalyzer result would have produced the same result.
We’ll have to wait and see how this, as I referred to it earlier, monumental blunder plays out in Massachusetts.
As predicted, recreational marijuana is here in California. California joined Nevada, Oregon, Washington, Colorado, Maine, Vermont, Massachusetts, and the District of Columbia in legalizing both medical and recreational marijuana. Thirty states and the District of Columbia have legalized medical marijuana. The trend of states in the expanding legalization of marijuana has had tech companies scrambling to become the first to develop a marijuana breathalyzer.
However, a California company has recently claimed to have cracked the code.
California Vehicle Code section 23152(e) makes it illegal to drive a vehicle while under the influence of drugs including marijuana. Unlike California’s DUI of alcohol law, there is no legal limit for marijuana, or more specifically, tetrahydrocannabinol (THC) the psychoactive component of marijuana. Therefore, a person can only be arrested and convicted of a marijuana DUI if the ingestion of marijuana impairs a person’s ability to drive a vehicle as a sober person would under similar circumstances.
To prove that a person is driving under the influence of marijuana, a prosecutor can use officer observations of driving patterns, observations during the traffic stop, performance on field sobriety tests, and the presence of THC in any blood test done.
Although THC can be detected in quantities of nanograms per milliliter of blood, the quantification is unlike alcohol in that the degree of impairment is unrelated to the amount of THC in a person’s blood. With alcohol, there is a fairly accurate correlation between a person’s blood alcohol content and how impaired they are. Therefore, unlike alcohol where prosecutors only need to prove that a person’s BAC was above a 0.08 percent, with marijuana, prosecutors can only prove that a person was “under the influence.”
Since “under the influence” is an extremely subjective standard, it is often very difficult to prosecute DUI of marijuana cases. This is especially true if the driver refused to perform the field sobriety tests and/or the officer did not observe driving that would be indicative of someone who is under the influence of marijuana.
Hound Labs, located in Oakland, California, is hoping to bridge the gap for officers and prosecutors.
“We are trying to make the establishment of impairment around marijuana rational and to balance fairness and safety,” said Hound Labs CEO Mike Lynn.
The company is claiming that it has developed a breathalyzer that can detect whether a subject has ingested marijuana in the last two hours, which many to consider the peak time for marijuana impairment after ingestion.
“When you find THC in breath, you can be pretty darn sure that somebody smoked pot in the last couple of hours,” Lynn says. “And we don’t want to have people driving during that time period or, frankly, at a work site in a construction zone.”
If accurate, Hound Labs would be the closest to developing this type of technology. However, thus far, no company has yet developed a machine to detect actual impairment.
According to Lynn, law enforcement are trying to determine who is impaired as opposed to “”somebody who smoked maybe yesterday or a few days ago and is not impaired. They’re not in the business of arresting people that are not impaired when it comes to marijuana. That makes no sense at all.”
Several law enforcement agencies will begin testing Hound Lab’s breathalyzer this fall. “They’re interested in it providing objective data for them at the roadside,” says Lynn. “That’s really the key, objective data at the roadside — just like we have for alcohol.”
For those of you who think that it is safe to smoke some marijuana and get behind the wheel, be aware that law enforcement could be out with a new roadside tool at their disposal to confirm that you have smoked within two hours, that is if Hound Labs’s new device does that it claims it can do.
Defense attorneys have been saying for years; breathalyzers are flawed. A new report that was never meant to be seen was and it confirms the defense attorneys’ suspicions.
Unsurprisingly, our story begins with a DUI case which arose out of Washington state. The DUI defense attorney in the case sought the assistance of two experts to analyze the breathalyzer’s source code accuracy in producing blood alcohol content results.
The experts determined that the source code used by the breathalyzer in the case, which happens to be the same breathalyzer used in other states including California, was fundamentally flawed by producing elevated blood alcohol content readings for reasons I’m not smart enough to understand. The experts put their findings into a preliminary report.
In 2017 at a DUI defense attorney conference, the experts shared their findings and the report with the attendees. This prompted the manufacturer of the breathalyzer to initiate legal action for violation of a protective order regarding the breathalyzer’s source code. The manufacturer and the experts settled out of court.
The experts are now tightlipped about the settlement and have walked back the contents of their report later claiming that it was incomplete, unfinished, and should not be relied upon by those few people who were in possession of it.
ZDNet, however, obtained at copy of the report and published an article detailing its contents and the implications it could have for thousands of DUI cases in a number of states, including California.
Researchers say a breathalyzer has flaws, casting doubt on countless convictions
May 10, 2018, ZDNet – The source code behind a police breathalyzer widely used in multiple states — and millions of drunk driving arrests — is under fire.
It’s the latest case of technology and the real world colliding — one that revolves around source code, calibration of equipment, two researchers and legal maneuvering, state law enforcement agencies, and Draeger, the breathalyzer’s manufacturer.
This most recent skirmish began a decade ago when Washington state police sought to replace its aging fleet of breathalyzers. When the Washington police opened solicitations, the only bidder, Draeger, a German medical technology maker, won the contract to sell its flagship device, the Alcotest 9510, across the state.
But defense attorneys have long believed the breathalyzer is faulty.
Jason Lantz, a Washington-based defense lawyer, enlisted a software engineer and a security researcher to examine its source code. The two experts wrote in a preliminary report that they found flaws capable of producing incorrect breath test results. The defense hailed the results as a breakthrough, believing the findings could cast doubt on countless drunk-driving prosecutions.
The two distributed their early findings to attendees at a conference for defense lawyers, which Draeger said was in violation of a court-signed protective order the experts had agreed to, and the company threatened to sue.
Their research was left unfinished, and a final report was never completed.
Draeger said in a statement the company was protecting its source code and intellectual property, not muzzling research.
“Pursuant to a protective order, Draeger provided the source code to both of the defense experts in Snohomish County,” said Marion Varec, a spokesperson for Draeger. “That source code is highly proprietary and it was important to Draeger that the protective order limit its use to the purposes of the litigation at issue.” Draeger says it believes that one of the experts entrusted to examine the source code was using it in violation of the protective order, so Draeger sent the expert a cease and desist letter. Draeger says it “worked with the expert to resolve the issue.”
Of the law firms we spoke to that were at the conference and received the report, none knew of Draeger’s threat to launch legal action. A person with a copy of the report allowed ZDNet to read it.
The breathalyzer has become a staple in law enforcement, with more than a million Americans arrested each year for driving under the influence of alcohol — an offense known as a DUI. Drunk driving has its own economy: A multi-billion dollar business for lawyers, state governments, and the breathalyzer manufacturers — all of which have a commercial stake at play.
Yet, the case in Washington is only the latest in several legal battles where the breathalyzer has faced scrutiny about the technology used to secure convictions.
TRIAL BY MACHINE
When one Washington state driver accused of drunk-driving in 2015 disputed the reading, his defense counsel petitioned the court to obtain the device’s source code from Draeger.
Lantz, who was leading the legal effort to review the Alcotest 9510 in the state, hired two software engineers, Falcon Momot, a security consultant, and Robert Walker, a software engineer and decade-long Microsoft veteran, who were tasked with examining the code. The code was obtained under a court-signed protective order, putting strict controls on Momot and Walker to protect the source code, though the order permitted the researchers to report their findings, with some limitations. Although the researchers were not given a device, the researchers were given a binary file containing the state’s configuration set by Washington State Patrol.
Although their findings had yet to be verified against one of the breathalyzers, their preliminary report outlined several issues in the code that they said could impact the outcome of an alcohol breath test.
In order to produce a result, the Alcotest 9510 uses two sensors to measure alcohol content in a breath sample: An infrared beam that measures how much light goes through the breath, and a fuel cell that measures the electrical current of the sample. The results should be about the same and within a small margin of error — usually within a thousandth of a decimal point. If the results are too far apart, the test will be rejected.
But the report said that under some conditions the breathalyzer can return an inflated reading — a result that could also push a person over the legal limit.
One attorney, who read the report, said they believed the report showed the breathalyzer “tipped the scales” in favor of prosecutors, and against drivers.
One section in the report raised issue with a lack of adjustment of a person’s breath temperature.
Breath temperature can fluctuate throughout the day, but, according to the report, can also wildly change the results of an alcohol breath test. Without correction, a single digit over a normal breath temperature of 34 degrees centigrade can inflate the results by six percent — enough to push a person over the limit.
The quadratic formula set by the Washington State Patrol should correct the breath temperature to prevent false results. The quadratic formula corrects warmer breath downward, said the report, but the code doesn’t explain how the corrections are made. The corrections “may be insufficient” if the formula is faulty, the report added.
Issues with the code notwithstanding, Washington chose not to install a component to measure breath temperature, according to testimony in a 2015 hearing, and later confirmed by Draeger.
Kyle Moore, a spokesperson for Washington State Patrol said the police department “tested and approved the instrument that best fit our business needs,” and believes the device can produce accurate results without the breath temperature sensor.
The code is also meant to check to ensure the device is operating within a certain temperature range set by Draeger, because the device can produce incorrect results if it’s too hot or too cold.
But the report said a check meant to measure the ambient temperature was disabled in the state configuration.
“The unit could record a result even when outside of its operational requirements,” said the report. If the breathalyzer was too warm, the printed-out results would give no indication the test might be invalid, the report said.
Draeger disputed this finding. A spokesperson said the Washington devices check their temperature, the check is enabled, and that the devices will not produce a reading while the device is outside its operational temperature range.
When asked, a Washington State Patrol spokesperson would not say if the breathalyzer was configured to allow breath tests outside its operational temperature range, saying only that the device “has been tested and validated in various ambient temperatures.”
The report also scrutinized the other sensor — the fuel cell — used to measure a person’s alcohol levels. Any fuel cell will degrade over time — more so when the breathalyzer is used often. This decay can alter the accuracy of test results. The code is meant to adjust the results to balance out the fuel cell’s decline, but the report said the correction is flawed. Breathalyzers should be re-calibrated every year, but the state’s configuration limits those adjustments only to the first six months, the report added.
“We also note that the calibration age does not account for the use frequency of conditions; a unit that has been used hundreds of times per day would have the same correction as one used only once or twice in several months,” the report said.
Concluding the nine-page report, the researchers say they are “skeptical” that the Alcotest 9510 can produce a reliable measurement of breath alcohol.
“Although the apparatus states its output in very absolute terms, we recommend interpreting the results with extreme caution,” the report said.
Although Momot and Walker’s code review was limited to devices in Washington, similar concerns dragged other states into protracted legal battles, forcing prosecutors to defend not only the breathalyzer but also how it’s configured.
But the line between Draeger’s source code and each state’s configuration is blurry, making it difficult to know who is responsible for incorrect results.
Draeger said in an email that the “calibration and adjustment procedures depend on the instrument, additional equipment and materials, and the persons performing these procedures.” When asked about the guardrails put in place to prevent calibration errors, the company said, “only trained and certified personnel perform special instrument certification procedures.”
Washington State Patrol said the device produces accurate results, even without certain sensors installed.
If source code gets into the wrong hands, the damage would be incalculable.
Draeger’s breathalyzer is widely used across the US, including in California, Connecticut, Massachusetts, New Jersey, and New York. It’s often the only breathalyzer used in the states where they were bought.
In both New Jersey and Massachusetts, defense lawyers raised concerns. By acquiring the devices used by the states, lawyers commissioned engineers to analyze the code who say they found flaws that they say could produce incorrect results.
But defense teams in both states largely failed to stop their state governments from using the devices, public records show.
New Jersey’s top court found in 2008 that a similar Alcotest breathalyzer — said to use the same underlying algorithms as the Alcotest 9510 — was “generally scientifically reliable” and can be used with some configuration changes. One such change was to adjust the breathalyzer’s results for women over age 60 — who often aren’t able to produce the minimum breath volume of 1.5 liters required for a test. But defense lawyers argued that these changes were never put into place.
The same court ruled five years later that the breathalyzer “remains scientifically reliable, and generates results that are admissible” in court.
In nearby Massachusetts, a scandal that blew up in 2017 involving alleged failings in the breathalyzer threw thousands of prosecutions into disarray, because “all but two of the 392 machines” examined in the state had not been properly calibrated.
A district judge ruled that breath test results from miscalibrated devices for two years prior to September 2014 were “presumptively unreliable,” said Joe Bernard, a defense attorney who led the case against the Alcotest 9510 in Massachusetts.
Bernard, and his colleague Tom Workman, a computer forensic expert who later trained as a lawyer and consulted on the case, obtained the state’s source code and produced a report.
In a phone call, Workman criticized the Draeger breathalyzer, arguing that it can produce widely inflated results. One section of his report claimed the device had a litany of programming errors, including code that — like in Washington — apparently fails to correct for fuel cell fatigue.
But the court rejected the findings and found the source code still produced sound scientific results.
“THROW CAUTION TO THE WIND”
While legal battles were ongoing, Washington waited to push ahead with its deployment, but the ruling in New Jersey case in 2008 was seen as a vote of confidence.
Almost a year later, Washington State Patrol’s toxicologist said in an email seen by ZDNet that the police department should “throw caution to the wind” to deploy the device to police officers across the state without commissioning an independent source code evaluation — though she recommended confirming with the chief of police.
When asked whether an independent evaluation was ever commissioned, a Washington State Patrol spokesperson would not comment further and referred back to the legal filings in the case.
A later email in 2015 confirmed that the Washington State Patrol “never commissioned” an independent evaluation.
Moses Garcia, a former Washington state prosecutor who now works for a non-profit providing local governments in the state with legal advice, said in an email that the earlier breathalyzer in the New Jersey case had already been deemed admissible, and that the newer Alcotest 9510 uses the “same basic algorithms and formulas” as its predecessor.
The former prosecutor criticized the defense’s discovery effort as “speculation.”
“In adopting and approving the [Alcotest 9510], the Washington breath alcohol program exceeds, by far, the scientific standards accepted in the scientific community for breath test instrument validation,” he said.
Five years after the contract was signed, Washington State Patrol began deploying hundreds of Draeger breathalyzers in 2014 — sparking interest from defense attorneys in the state.
Not long after, defense attorneys in the state sought access to the devices.
Lantz was granted access to the source code used for Momot and Walker’s code review by a local county court. In one of several recent phone calls with ZDNet, he recounted how he set out to see if there were problems with the state’s device.
“We thought we would find something but nothing like this,” he said.
SETTLEMENTS AND SETBACKS
Hundreds of DUI lawyers descended on Las Vegas in mid-2017 for their annual gathering.
At the event, the two researchers shared their findings, which claimed the Alcotest 9510 having a “defective design.”
Word spread quickly. Draeger sent the researchers a cease and desist letter claiming defamation and alleging the two violated a protective order, designed to protect the source code from leaking.
Draeger and the researchers settled before a case was filed in court, avoiding any protracted legal battle. A legal case disputing the fine print of the order could have taken years to resolve.
Draeger said it “remains willing to provide the source code for use in other litigation in Washington, so long as a proper protective order is in place.”
The statement said that the two experts “never intended to violate the protective order” and denied any wrongdoing. But the two sides “agree” the draft report was based on incomplete data and not finished — and that “no one in possession of the report should rely on it for any purpose.”
We reached out to Walker with questions, but he referred only to the settlement statement on his company’s website, and he declined to comment further.
Draeger would not say why the settlement did not include a retraction on the report’s findings.
“There has not been an evidentiary hearing in Washington. If and when there is one, Draeger will cooperate fully,” a spokesperson said.
But Lantz paints a different picture. The defense attorney said he believes there “really was no technical violation of the protective order,” because the report didn’t disclose any source code.
“I do believe that [Draeger] is trying to interpret the protective order to be something that it’s not,” he said. “If we could go back in time, I would’ve asked that the report was not handed out — just because of the optics of it.”
Lantz said the protective order is vague, but contends it was framed to prevent the researchers from using the source code or their findings for commercial gain — effectively preventing Momot and Walker from using their knowledge to build their own competing devices. He believes the order gives Draeger near complete control over the code and anything the company deems “protected” information.
That’s when Draeger “began developing a strategy on how to block” the researchers’ report, said Lantz, because the company didn’t want the “pervasive exposure of these flaws.”
“I believe that interest of Draeger’s to protect their bottom line overlaps with the state’s interest to keep juries from hearing this information about the problems,” he said.
Draeger maintained that it is protecting its intellectual property. The company said in response that it “takes very seriously the proprietary nature of its source code,” and “protects proprietary information as a sound business practice,” which can include various types of communications or agreements for a particular matter.
Momot and Walker are no longer involved with the case, but Sam Felton, a Washington-based software engineer, is set to conduct another review of the Alcotest 9510 code. When contacted, Felton would not speak in specifics about his findings to date, citing his own protective order, except that he found things in the code that caused him “to have concerns.”
And Lantz, now at a new law firm, is working on starting discovery proceedings in neighboring King County, home of Seattle, the largest city in the state.
According to the American Lung Association, Chronic Obstructive Pulmonary Disease, commonly referred to as COPD, which includes chronic bronchitis and emphysema, is a chronic lung disease that makes it difficult to breathe. And according to the World Health Organization, COPD affects 65 million people worldwide. COPD, however, affected one Canadian woman in an unexpected way; it caused her to fail a breathalyzer.
Connie McLean, a 64-year-old woman from New Brunswick, Canada, who suffers from COPD, said that the condition can make everyday living difficult.
“When I’m carrying in wood, I can only carry in a couple sticks at a time and I usually have to stop and get some air before I go and get some more,” she said last week. “And shoveling is even worse.”
Early last month, McLean was pulled over by local law enforcement. The officer asked her if she had been drinking. McLean responded that she had a beer that afternoon. At that point, the officer produced a breathalyzer to try and determine her blood alcohol content.
As a result of the COPD, McLean could not produce a strong enough of a breath sample to provide a breathalyzer reading.
“I tried several times, but due to COPD and mucous in my airway I wasn’t successful,” she said. “And he just almost hollered, ‘You’re not trying, you’re under arrest and you’re going to jail.’”
McLean was charged with refusing to comply with the breathalyzer test which resulted in her vehicle being impounded for 30 days and her driver’s license being suspended for 90 days.
“It makes perfect sense to us that if you have severe COPD that it would be impossible to exhale for any length of time,” said Henry Roberts of COPD Canada. “I would hope the police would show some compassion to people who have difficulty breathing.”
McLean has a court date next month and intends on fighting the charge.
McLean’s predicament is not an unusual one, even here in the United States. Often, people are unable to provide a sufficient breath test for a number of health-related reasons. Breathalyzers require deep lung air, known as alveolar air, to be able to produce a blood alcohol content reading. If a person does not advise an officer of the health issue that might prevent them from providing alveolar air, the officer may believe that the person is deliberately trying to provide a sufficient breath sample.
California courts have found that an inference can be made that a person is deliberately attempting to avoid providing a sufficient breath sample if the facts permit. If such an inference is made, the court treats it as a refusal.
Fortunately, here in California, a driver is not required to give a breath sample for a roadside breathalyzer, commonly referred to as a “preliminary alcohol screening” test or “PAS” test. Refusing it will not result in additional penalties with either the court or the DMV. In fact, many DUI attorneys like myself recommend politely refusing the PAS test.
Of more importance, however, is the mandatory “chemical test” under California’s “implied consent law.” Under the implied consent law, a driver must submit to a chemical test once they are lawfully arrested on suspicion of a DUI. The chemical test can be either a breath or a blood test. Only for a refusal of the chemical test, not the PAS test, may a driver be punished.
Here in the California, a refusal of a chemical test can result in jail time, a longer DUI program, and/or a longer license suspension.
Let’s hope that reason prevails in the Canadian courts for McLean’s sake.
Thanks to my student, David Hong, for sending me this story!
This past August, the Colorado Department of Transportation gave 475 personal smartphone breathalyzers to people who had been convicted of a DUI. In addition to the obvious objective of preventing drunk driving, the Colorado Department of Transportation also wanted to see if, in fact, having the breathalyzer actually helped keep them from driving drunk again.
After recently surveying those people who were given breathalyzers, the Colorado Department of Transportation’s results showed that having a personal breathalyzer helped those people avoid driving drunk. In fact, a whopping 90 percent said that having a breathalyzer helped them avoid driving drunk and 94 percent said that they would recommend a personal breathalyzer to others who regularly drink alcohol.
The Colorado Department of Transportation teamed up with BACtrack, who created the smartphone breathalyzer, during the informal study. The breathalyzer is linked to a smartphone app through Bluetooth. If the user determines that they cannot legally drive, the smartphone app can order them a taxi or Uber.
I’ve written a few times on the benefits of purchasing a personal breathalyzer.
Like those handed out by the Colorado Department of Transportation, people can buy breathalyzers that can either be attached directly to a smartphone or connect to smartphone through Bluetooth and will run buyers between $100 and $150.
Other, less expensive, breathalyzers can come on keychains and can cost buyers as low as $15. Like many things, quality comes with price and the results of these novelty breathalyzers are questionable at best and decrease in accuracy after time.
Some breathalyzers are handheld and resemble those commonly associated with the breathalyzers used by law enforcement. Those breathalyzers range widely in terms of price and quality. Some come as low as $50 and some can go as high as a few hundred dollars. Obviously, the less expensive handheld breathalyzers have lower quality, but those more expensive handheld breathalyzers are the ones used by law enforcement because of their accuracy and may even be approved by the Food and Drug Administration (FDA). Law enforcement grade breathalyzers have an accuracy range of plus or minus 0.002 percent which means that if a person is a 0.08 percent, the breathalyzer results can range between 0.078 percent and 0.082 percent.
I purchased my own personal handheld breathalyzer to experience first-hand what I’ve been writing about. I didn’t break the bank, but I did spend $60 on the lower end of the legitimate handheld breathalyzers. After having a few drinks, I gave it a go. While I don’t know what my actual blood alcohol content was because different readings were provided, I can say that the multiple readings ranged by about 0.03 percent. In other words, using that range, a person could register between a 0.095 percent and 0.65 percent, or between a 0.18 percent and 0.12 percent, or between 0.26 and 0.23 percent. After a few months of use, the breathalyzer stopped working and I need to send it to the manufacturer.
While on the face of it, it might seem as though this range is too large to help drivers know whether they are okay to drive because if a person is actually at a 0.08 percent, the breathalyzer reading can show results as high as 0.095 percent and as low as 0.065 percent. Having said that, if a person knows that a breathalyzer is less than accurate and shows a blood alcohol content of 0.065 percent, they may know that they might actually be at a 0.08 percent and abstain from driving. And bear in mind that this is one of the less accurate handheld breathalyzers.
At a minimum, having a personal breathalyzer might help people bridge the gap between how a person perceives what their intoxication level is and what their blood alcohol content is. And while many breathalyzers might not provide an accurate reading, it might still prevent people from driving merely knowing that they are close to the limit. And knowing a range is certainly better than knowing nothing and making a stupid guess.