Breathalyzers, BAC Devices, and What They Really Mean in an Arizona DUI Case
Understanding keychain breathalyzers, portable police breath tests, and the Intoxilyzer 9000 in Tucson & Pima County
Even though most people have heard of a “breathalyzer,” very few understand that not all breath-testing devices are the same. In fact, the device you see on Amazon, the portable breath test an officer uses on the roadside, and the Intoxilyzer 9000 machine used for official police testing operate very differently—and they carry very different levels of legal weight in Arizona DUI cases.
If you were recently arrested for DUI in Tucson or anywhere in Pima County, you may already be trying to make sense of what the breath test in your case actually means. This post walks through every major type of breath-testing device, explains which results are admissible in Arizona courts, and shows why breath test numbers are far more complex—and far more challengeable—than most people realize.
1. Consumer Breathalyzers (Keychain and Smartphone Devices)
Over the last decade, the market exploded with small, inexpensive devices people can purchase online: keychain breathalyzers, handheld units marketed for “self-monitoring,” and even versions that sync with a smartphone app.
How These Devices Work
Most rely on simple fuel-cell sensors or semiconductor technology. They are extremely sensitive to:
Temperature changes
Mouth alcohol (e.g., alcohol in the mouth that hasn’t been absorbed into the bloodstream)
Residue from food, breath mints, or even hand sanitizer
Calibration frequency (which most consumer devices rarely receive)
Accuracy Problems
These devices can sometimes give a ballpark estimate, but they simply are not designed for law-enforcement reliability. Variations from unit to unit, battery level, and sensor drift mean the numbers are often inconsistent.
Legal Effect in Arizona DUI Cases
Consumer devices have zero admissibility or evidentiary value in court. A reading from a pocket device cannot be used to prove impairment, and it cannot be used to establish a BAC. These devices are purely personal-use tools, and even then, they have significant limitations.
2. Remote Alcohol Monitoring Devices (Soberlink, CAM, SCRAM)
For people on pretrial release, probation, or involved in family-court matters, courts sometimes require continuous alcohol monitoring. Devices like Soberlink or SCRAM CAM bracelets are designed for supervision—not criminal prosecution of DUI.
How They Work
Soberlink: A handheld remote breathalyzer with facial recognition and real-time reporting.
SCRAM CAM: A wearable ankle bracelet that measures transdermal alcohol concentration every 30 minutes.
Purpose
Courts use these to ensure compliance with “no alcohol” conditions. Family courts sometimes use them for custody or parenting-time disputes.
Legal Effect
These devices do not replace the state’s evidentiary breath test. They are not admissible to prove DUI BAC levels, and they do not satisfy Arizona’s statutory requirements for criminal conviction evidence.
3. Portable Breath Tests (PBTs) Used by Police Officers
If you are stopped on the side of the road, an officer may ask you to blow into a small handheld device. In Arizona, this is known as a Portable Breath Test or PBT.
Purpose of a PBT
A PBT is used only to help the officer establish probable cause for arrest—not to prove your BAC in court.
How a PBT Works
PBTs use a small fuel-cell sensor that attempts to estimate alcohol content in the breath. However, these devices:
Are not calibrated with the same rigor as evidentiary machines
Are highly sensitive to mouth alcohol
Can be affected by temperature, contamination, burping, acid reflux, and even diabetes (ketones)
Have significant margins of error
Arizona Law on PBT Admissibility
Under Arizona law:
➡ A PBT is not admissible in court to show a BAC number.
➡ The prosecutor may only introduce evidence that alcohol was present, not the specific numerical result.
This is critical. A roadside BAC of “0.11” on a PBT cannot be used to convict you. Only the full evidentiary test counts.
4. The Intoxilyzer 9000 (Arizona’s Official Breath Testing Machine)
Arizona uses the Intoxilyzer 9000 (often called the “Inox”) as its evidentiary breath-testing instrument. This is the machine located at police stations, sheriff sub-stations, and DUI testing facilities.
How the Intoxilyzer 9000 Works
The device uses infrared spectroscopy to measure ethyl alcohol molecules in deep lung air. In theory, it isolates the specific wavelength absorbed by ethanol and calculates a corresponding BAC.
Legal Admissibility in Arizona
The only admissible breath test results in Arizona DUI cases are:
Tests performed on the Intoxilyzer 9000
Conducted by a certified operator
With all statutory and regulatory requirements satisfied
If your DUI case includes a breath test, this is the machine that matters.
5. What Must Happen for an Intoxilyzer 9000 Result to Be Valid?
Arizona’s rules for breath test admissibility are strict. A prosecutor cannot simply introduce a BAC number without showing the machine, procedure, and operator complied with very specific requirements.
A Valid Test Requires:
1. A 15-Minute Observation (Deprivation) Period
The operator must observe you continuously to ensure:
No burping
No vomiting
No drinking
No foreign substances in the mouth
Any of these can introduce “mouth alcohol,” causing falsely elevated numbers.
2. Machine Calibration and Control Tests
Arizona requires:
A valid calibration test
Regular maintenance records
Proper certification of the machine
A functioning internal standard
If the machine fails control tests or hasn’t been maintained correctly, results can be challenged.
3. A Proper Warm-Up and Diagnostic Sequence
The Intoxilyzer 9000 runs an internal diagnostic check before any test. If this sequence is interrupted or fails, the results are not valid.
4. Two Breath Samples Within the Required Variance
Arizona law requires two samples.
They must:
Be within 0.020 of each other
Not show evidence of sensor interference
Not display “slope” issues indicating mouth alcohol or irregular breath patterns
If the numbers are outside the acceptable range, the test should not be admitted.
5. A Certified Operator
Officers must hold a valid permit specific to the machine. Failure to follow training or protocol creates admissibility problems.
6. Challenging the Intoxilyzer 9000 in Tucson & Pima County
Even though the Intoxilyzer 9000 is Arizona’s accepted evidentiary machine, breath testing is far from infallible, especially in Tucson and Pima County. Defense attorneys frequently challenge breath test evidence based on scientific, medical, and procedural issues.
Why Breath Testing Is Not Widely Used in Tucson
Many agencies in Southern Arizona rely more heavily on:
Blood draws, or
DRE (Drug Recognition Evaluator) investigations
Blood is often preferred for serious DUI cases because:
It measures actual alcohol in the bloodstream
It can detect drugs (PBTs and breath machines cannot)
It reduces the risk of procedural challenges
Some agencies barely use the Intoxilyzer at all because the machine’s reliability can be successfully challenged under the right circumstances.
Common Defense Challenges
1. Variability in Human Physiology
Breath testing assumes all humans share identical characteristics. They don’t.
Factors affecting results include:
Height
Weight
Sex
Body temperature
Breathing pattern
Sinus conditions
GERD
Lung capacity
These differences cause significant variability between breath alcohol and blood alcohol.
2. Partition Ratio Problems
Breath testing assumes a 2100:1 partition ratio, meaning 1 part alcohol in the breath equals 2100 parts in the blood.
But in reality, partition ratios vary:
From 1100:1 to 3000:1
Person to person
Minute to minute
This can cause breath testing to over-report BAC, especially in smaller individuals or those with higher body temperature.
3. Metabolism & Elimination Rates
Widmark’s formula, elimination curves, and metabolic factors demonstrate that alcohol absorption is not linear. Breath testing during the absorption phase often yields artificially high readings.
4. Interfering Compounds
Acetone in diabetics, ketones from fasting, and even certain diets (low-carb/keto) can create elevated readings.
5. Improper Observation Period
This is one of the most common issues. Officers may be filling out paperwork, talking to others, or multitasking while supposedly observing the driver.
Lack of continuous observation invalidates the test.
7. Breath Test vs. Blood Test: Why Police Make Different Choices
Many people assume breath tests are the standard nationwide, and in many states they are. But Arizona’s enforcement varies by county.
Breath Tests Are Less Common in Tucson
Agencies like:
Tucson Police Department
Pima County Sheriff’s Department
Oro Valley
Sahuarita
Marana
often rely heavily on blood testing.
Why?
Blood is more precise
Blood measures both alcohol and drugs
Blood evidence withstands challenges better
Hospitals and EMTs are readily available for draws
Breath tests, while faster, simply create too many potential issues for prosecutors in borderline cases.
8. Why the Type of Breath Test Matters for Your Defense
Understanding what kind of device was used in your case is crucial.
If it was a PBT on the roadside:
That number cannot be used against you.
If it was the Intoxilyzer 9000:
The admissibility depends entirely on whether proper procedure was followed.
If no breath test was done at all:
That opens an entirely different line of defense involving driving patterns, officer observations, field sobriety tests, and toxicology.
A skilled DUI lawyer knows how to identify the weaknesses in breath testing, challenge reliability, and use the science to your advantage.
9. Final Thoughts: Breath Tests Are Just One Piece of the Puzzle
Breath testing can sound simple—blow into the device, get a number—but in Arizona DUI defense, the number is only the beginning of the story.
Understanding whether the police used:
A PBT
An Intoxilyzer 9000
A blood draw
Or no chemical test at all
shapes the entire defense strategy.
In Tucson and Pima County, breath tests are often less reliable, less consistent, and more challengeable than most people realize. A strong defense evaluates:
The device
The operator
The scientific assumptions
The procedure
The human physiology
The timing
And the law
No two DUI cases are the same, and even the highest-tech machine cannot replace individualized analysis by an experienced defense attorney.
If you were charged with DUI in Tucson or Pima County, you do not have to navigate this alone
I’ve handled hundreds of DUI cases in Southern Arizona, including cases involving the Intoxilyzer 9000, blood tests, refusals, and complex impairment allegations. My practice focuses on identifying weaknesses in the state’s evidence and building strong, science-based defenses for my clients.
If you have questions about the breath test in your case—or whether the state’s evidence is reliable—reach out anytime. Having answers early can make a powerful difference.
