The DataMaster breathalyzer’s accuracy is governed by a published standard of plus or minus 5 percent or 0.005 grams per 210 liters at each test concentration, and in practice its readings hold up in court when the device has been calibrated on schedule, the operator followed the observation and sampling procedure, and the two required breath samples agree. When any of those conditions slip, the reading becomes vulnerable to challenge. The machine is widely used across American law enforcement to measure breath alcohol concentration against the 0.08 legal limit for drivers 21 and older, and a reading at or above that number carries real weight with a judge or jury. It is not, however, unchallengeable evidence.
What the Machine Actually Measures
The DataMaster identifies ethanol by shining infrared light through a breath sample and measuring how much is absorbed. Alcohol molecules absorb infrared energy at predictable wavelengths, and the device uses filters tuned to 3.37 and 3.44 microns.1Washington State Patrol. Mathematical Determination of Breath Alcohol Concentration in the BAC Verifier DataMaster Using two wavelengths rather than one lets the software distinguish ethanol from other compounds that absorb infrared light at overlapping wavelengths, which is the main reason modern evidential testers are harder to fool with substances like acetone than their predecessors were.
What the detector picks up is light absorption. What the printout shows is a blood alcohol concentration. The step between those two is a mathematical conversion, and that conversion is where the first accuracy question lives.
The 2,100-to-1 Ratio and Individual Variation
Every evidential breath tester converts breath to a blood-equivalent number using a fixed ratio of 2,100 to 1. The assumption is that 2,100 milliliters of deep lung air contains the same amount of alcohol as 1 milliliter of blood. That ratio was adopted decades ago when the original Breathalyzer was developed, and it became the foundation for the legal limit of 0.08 grams per 210 liters of breath.
The ratio varies from person to person. A controlled study of 100 volunteers across multiple ethnic groups found the average post-absorptive ratio was 2,382 to 1, with a standard deviation of about 119, and no participant fell below 2,100 to 1 during the post-absorptive phase.2PubMed Central. Reflections on Variability in the Blood-Breath Ratio of Ethanol and Its Implications If your personal ratio is higher than 2,100 to 1, the machine understates your true blood alcohol level. If it is lower, the machine overstates it. Other countries use different numbers for their legal standards, ranging from 2,000 to 2,400, which tells you there is no international consensus on the correct value.
The DataMaster does not measure your individual ratio. It applies 2,100 to 1 to everyone. Defense attorneys sometimes raise this point when a reading lands right at or just above the limit, arguing the fixed ratio introduces enough uncertainty to create reasonable doubt.
Calibration and the Accepted Accuracy Standard
An uncalibrated DataMaster is an expensive box that prints numbers, and no court will accept its output without documentation showing the device was accurate when it tested you. Calibration involves running known alcohol standards through the machine and confirming the readings fall within an acceptable margin.
Technicians use either wet-bath simulators or dry gas canisters containing a certified alcohol concentration, commonly 0.080 or 0.100 grams per 210 liters. The simulator solution must be heated to 34 degrees Celsius to mimic the temperature of exhaled breath, because temperature affects how much alcohol evaporates from the solution into the vapor the machine samples. A one-degree increase in breath temperature can shift the reading by roughly 7 percent, so this is not a minor detail.
The accuracy standard from the American Academy of Forensic Sciences requires readings to fall within plus or minus 5 percent or 0.005 grams per 210 liters, whichever is greater, at each test concentration.3American Academy of Forensic Sciences. ASB Standard 055 – Standard for Breath Alcohol Calibration Calibration intervals cannot exceed 12 months, and many agencies calibrate more often. A device that fails its accuracy check is pulled from service until a certified technician repairs and recalibrates it. Every calibration result, solution change, repair, and accuracy test is logged in the instrument’s permanent maintenance file, and defense attorneys can subpoena those records.
The Observation Period and Mouth Alcohol
Before the test, the officer must watch you continuously for a set period, typically 15 to 20 minutes depending on the jurisdiction. The purpose is to make sure nothing in your mouth artificially inflates the reading. If you belch, vomit, eat, drink, smoke, or put anything in your mouth during that window, residual alcohol can linger in your oral cavity and produce a reading that reflects mouth alcohol rather than deep lung air.
Mouth alcohol is the single biggest source of falsely elevated breath test results. When you burp or experience acid reflux, alcohol vapor from your stomach can travel into your throat and mouth, and if you blow into the machine with that vapor still present, the sensor reads it along with the lung alcohol. The observation period gives that residual alcohol time to clear.
Observation must be continuous. Officers can set up equipment or fill out paperwork, but they cannot lose visual contact with you for any meaningful stretch. If the officer looks away and you belch unnoticed, the scientific basis for the observation period collapses. When a contaminating event does occur during the watch, the clock resets to zero and the full period starts over. Courts have suppressed breath test results where defense attorneys showed the officer was distracted, left the room, or failed to maintain genuine continuous observation.
The Duplicate-Sample Check
The DataMaster takes two breath samples, not one, and the two results must agree within a specified tolerance, most commonly either an absolute difference of no more than 0.020 grams per 210 liters or within plus or minus 10 percent of their mean. If the samples do not agree, the results are invalid and the test must be readministered. Between the samples, the machine runs an air blank to purge the chamber and confirm the baseline reads zero.
The machine also monitors the volume and flow rate of each breath to ensure it captures deep lung air. Most jurisdictions require a minimum sample of 1.1 to 1.5 liters sustained for roughly 4 to 5 seconds. Insufficient volume is recorded as an incomplete attempt, and after repeated failures the operator may document the situation as a refusal.
This duplicate-sample requirement is one of the strongest built-in safeguards against a single anomalous reading being used as evidence. It also limits the role of transient interference. Radio frequency interference from the radios common in police stations has been studied extensively; a 13-year retrospective analysis of over 26,000 breath tests found RFI messages in fewer than 0.48 percent of tests and no evidence that undetected RFI affected calibration checks or subject results.4ResearchGate. Radio Frequency Interference Messages During Breath Testing of Suspected Impaired Drivers For undetected interference to matter, it would need to affect both samples identically.
Medical Conditions and Other Interferents
The dual-filter design handles most common interferents, but a few medical and dietary situations come up often enough to address.
Acetone, Diabetes, and Low-Carb Diets
People with uncontrolled diabetes or those on very low-carbohydrate diets can produce elevated acetone in their breath as the body burns fat. Acetone absorbs some infrared light at wavelengths near those used to detect ethanol, which gave single-wavelength instruments trouble historically. Testing of seven evidential breath analyzers found devices using single-wavelength infrared spectroscopy showed no unacceptable responses to acetone at concentrations up to 350 micrograms per liter, and researchers concluded acetone was not a significant problem for breath alcohol analysis in traffic enforcement.5PubMed. Response of Breath-Alcohol Analyzers to Acetone: Further Studies The DataMaster’s two wavelengths reduce the risk further, though the issue remains a reasonable question for anyone with a metabolic condition producing unusually high acetone levels.
GERD
Gastroesophageal reflux disease is one of the most commonly raised medical defenses in DUI cases, on the theory that stomach contents carrying alcohol vapor into the mouth could inflate a breath reading. The research is less supportive than many defendants hope. A study using the DataMaster tested 10 subjects with severe GERD, provoking gastric reflux during testing with an abdominal compression belt. Four subjects experienced confirmed reflux, and the researchers found no widely deviant breath alcohol readings compared to actual blood alcohol levels when samples were taken at five-minute intervals. The study concluded the risk of stomach alcohol falsely increasing an evidential breath test result due to gastric reflux is “highly improbable.”6PubMed. Reliability of Breath-Alcohol Analysis in Individuals With Gastroesophageal Reflux Disease The sample was small, and defense experts still raise GERD in individual cases, particularly where the observation period may not have been properly conducted.
How Readings Are Challenged in Court
A DataMaster reading is powerful evidence, but it is open to attack along several well-established lines. The success of those challenges usually comes down to whether the prosecution can produce complete documentation.
- Calibration and maintenance records. A missed calibration, a failed accuracy check that was not properly addressed, or gaps in the log make every test conducted during that period questionable. Defense attorneys routinely subpoena the full maintenance history of the specific instrument that tested their client.
- Observation period violations. If officer testimony or dashcam footage shows the observation was not continuous, or a contaminating event occurred without a reset, the result can be challenged as scientifically unreliable and potentially excluded.
- Operator certification. The person administering the test must have been properly trained and certified at the time. Expired certifications or incomplete training records create an opening for suppression.
- Medical conditions. The research on GERD and acetone is less dramatic than defense marketing suggests, but a genuine medical condition combined with procedural gaps can create reasonable doubt, particularly when the reading is close to the limit.
- Rising blood alcohol. Alcohol absorption continues after your last drink. If there was a significant delay between the stop and the test, your blood alcohol at the time of driving may have been lower than the station reading. The argument works best when the timeline is well documented.
The common thread in successful challenges is paperwork. Agencies that keep meticulous records make it difficult to challenge their instruments. The ones that do not hand defense attorneys a roadmap.
Refusing the Test Is Not a Free Pass
Every state has an implied consent law, meaning that by driving on public roads you have already agreed to submit to chemical testing if lawfully arrested on suspicion of impaired driving.7NHTSA. BAC Test Refusal Penalties Refusing an evidential breath test does not avoid consequences; it triggers a separate set that often stacks on any DUI charge.
The most immediate is administrative license suspension, which happens through the motor vehicle agency rather than a criminal court. First-refusal suspensions range from 30 days to 18 months across states, with most falling between 6 months and one year. Second and later refusals bring longer suspensions, sometimes measured in years, and they take effect regardless of whether you are ultimately convicted of DUI.
A growing number of states also treat refusal as a criminal offense or use it to enhance the underlying DUI penalties. In some jurisdictions a second refusal is a misdemeanor carrying jail time. Others impose mandatory minimum sentences on the DUI conviction when refusal is involved. Several states require installation of an ignition interlock device as a condition of regaining any driving privileges. Fines, reinstatement fees, higher insurance premiums, and interlock costs mean refusal often ends up costing more than taking the test would have.
Your Right to an Independent Test
Most states give you the right to obtain an independent chemical test at your own expense after the police test is complete, typically a blood draw at a hospital or medical facility of your choosing. The officer generally cannot interfere, though the burden is on you to arrange and pay for it. Officers are not always required to tell you this right exists, so knowing about it in advance is the only reliable way to use it.
An independent blood test creates a second data point. Because blood testing measures alcohol concentration directly rather than through a breath-to-blood ratio, it can be more precise, and a result significantly lower than the breath reading gives a defense attorney concrete evidence to challenge the machine. Time matters: alcohol metabolism continues while you wait, so the longer the gap between the breath test and the blood draw, the less useful the comparison. If you are going to request an independent test, do it immediately.