Challenging the Field Sobriety Tests in Phoenix
The roadside “tests”, follow the pen, walk the line, stand on one leg, feel scientific. They are subjective, voluntary, and easy to fail sober, and they must follow strict NHTSA rules to mean anything at all.
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Are field sobriety tests accurate in Arizona?
Quick answer: Not very. Even when administered perfectly, the three standardized tests are only partially reliable, and they are voluntary in Arizona. Nerves, medical conditions, footwear, road conditions, age, and weight all cause “clues” in sober people. If the officer deviated from the NHTSA protocol, the results are essentially worthless, and we show the jury why.
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Former Prosecutors · Law Enforcement · Public Defenders
When you call Tamou Law Group, you reach a firm that handles criminal defense exclusively, with serious experience defending DUI cases across Arizona. Our team includes former prosecutors and law enforcement officers, so we know exactly how the State builds these cases, and where they fall apart.
At many large firms, the name on the building is a marketing figurehead, you rarely get them on the phone and your case goes to a junior associate. When you hire Tamou Law Group, your case is handled by a full team of attorneys, not associates, including Michael Tamou.
Designed to Build a Case Against You
Field sobriety tests are not neutral, they exist to justify an arrest.
The Standardized Field Sobriety Tests (SFSTs), Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn, and the One-Leg Stand, are the officer’s tool to build probable cause. They are graded on subjective “clues,” and even under ideal conditions their accuracy is limited. In the real world, at night, on the roadside, they are far worse.
In Arizona these tests are voluntary. You can decline them without an automatic penalty, and declining denies the officer this evidence, but if you took them, we can still take the results apart.
How Each Test Fails
Each standardized test has known weaknesses and strict administration rules.
We evaluate each test against the NHTSA manual:
- HGN (eye test), involuntary eye jerking has many innocent causes (fatigue, medications, neurological conditions), and it is frequently administered incorrectly.
- Walk-and-Turn, an unnatural task affected by nerves, footwear, uneven pavement, weight, age, and injury.
- One-Leg Stand, balance is impaired by countless non-alcohol factors, and the scoring is subjective.
- Non-standardized tests, finger-to-nose, alphabet, counting, have no scientific validation at all.
Body-camera footage often shows a person performing far better than the report claims, another reason the paper trail and video matter.
The NHTSA Protocol: Do It Wrong, Lose It
The tests are only valid if administered and scored exactly by the book.
NHTSA’s own research says the SFSTs are reliable only when administered and scored precisely as standardized. Officers routinely deviate, wrong instructions, wrong scoring, bad conditions, and each deviation undercuts the result.
A defense expert compares the officer’s administration to the NHTSA standard step by step and shows the jury exactly where it went wrong, and why the “clues” do not mean what the State claims.
The Standardized Tests, Their Accuracy & Their Flaws
Even done perfectly, the roadside tests are only partly reliable, and they are voluntary.
The Three NHTSA-Standardized Tests
- Horizontal Gaze Nystagmus (HGN), the eye test, best-case ~77% reliable.
- Walk-and-Turn, best-case ~68% reliable.
- One-Leg Stand, best-case ~65% reliable.
- Everything else (alphabet, counting, finger-to-nose) is non-standardized and unvalidated.
Innocent Reasons People “Fail”
- Nerves, fatigue, age, weight, and injuries.
- Footwear, uneven pavement, traffic, wind, and poor lighting.
- Medical conditions and medications causing nystagmus or imbalance.
- Improper administration, wrong instructions or scoring by the officer, which voids the result under NHTSA.
Turning “Failed” Into Doubt
Discredit the roadside tests and the arrest itself may be in question.
If the field sobriety tests were improperly given or are explained by innocent factors, they lose their weight, and the probable cause for the arrest can be challenged, which can suppress everything that followed.
Part of a full defense, see the Top 10 DUI defenses and Phoenix DUI defense. Call 623-321-4699, 24/7.
The Experts We Bring to DUI Cases
A DUI is a science case. We bring the specialists who take the State’s numbers apart, click any to see how.
Forensic Toxicologists
BAC & Absorption
Independently review the blood and breath results, the absorption curve, and whether the alleged number reflects your true level at the time of driving.
Breath-Test Analysts
Intoxilyzer & Calibration
Examine the machine’s calibration and maintenance logs and the 15-minute observation, exposing mouth alcohol, radio interference, and operator error that inflate readings.
Blood & Lab Experts
Gas Chromatography
Audit the blood draw, storage, fermentation risk, lab protocol, and reported uncertainty, where applying the margin of error can drop the reading below the threshold.
Medical Experts
GERD, Diabetes & Diet
Explain how acid reflux, diabetes, and low-carb diets can push a breath reading upward, independent of how much alcohol was actually consumed.
Field Sobriety Experts
NHTSA Protocol
Evaluate whether the standardized field sobriety tests were administered and scored correctly, and whether the “clues” really show impairment.
Records & Discovery Specialists
Maintenance & Logs
Pull the full calibration history, repair records, and the discovery the State would rather not produce, the paper trail that often reveals an unreliable machine.
Awards & Recognition
Our recognition for Phoenix DUI defense is independently verified, click any award to confirm it:
- National Trial Lawyers Top 100
- National Trial Lawyers Top 40 Under 40
- Elite Lawyer 2026 – Criminal Defense
- Super Lawyers – Southwest
- National College for DUI Defense (NCDD)
When you are looking for the best Phoenix DUI lawyers, these are the independently verified credentials that matter, earned by Founding Attorney Michael Tamou and a full team of attorneys, including former prosecutors.
Phoenix DUI Defense FAQs
Quick answers to the questions we hear most.
Are field sobriety tests mandatory in Arizona?
No. The roadside field sobriety tests are voluntary, and you can politely decline them with no automatic penalty. They exist mainly to build probable cause to arrest you.
Can you fail a field sobriety test while sober?
Easily. Nerves, medical conditions, injuries, age, weight, footwear, and road and lighting conditions all produce the “clues” officers score, with no alcohol involved.
What are the three standardized field sobriety tests?
Horizontal Gaze Nystagmus (the eye test), the Walk-and-Turn, and the One-Leg Stand. Only these three are NHTSA-standardized, and even they are only partially reliable when done perfectly.
What happens if the officer administered the test wrong?
NHTSA says the tests are valid only if administered and scored exactly as standardized. Deviations undercut the results and can be used to challenge probable cause for the arrest.
Do non-standardized tests count?
Tests like reciting the alphabet, counting, or finger-to-nose have no scientific validation and carry little weight. We highlight that lack of validity for the jury. Call 623-321-4699, 24/7.
Key Takeaways
- Field sobriety tests are subjective, voluntary, and easy to fail while sober.
- The three standardized tests (HGN, Walk-and-Turn, One-Leg Stand) are only partly reliable at best.
- NHTSA says results are valid only when administered and scored exactly by protocol.
- Non-standardized roadside tests have no scientific validation.
- Discrediting the tests can undermine the arrest itself. Call 623-321-4699, 24/7.
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Case Results Disclaimer: The results described on this page are based on specific facts and circumstances and do not guarantee or predict a similar outcome in any future case. Every case is different. Past results do not guarantee future results. No attorney-client relationship is formed by viewing this page or submitting a contact form until a written fee agreement has been signed. Tamou Law Group, PLLC is licensed to practice law in the State of Arizona. This website is for informational purposes only and does not constitute legal advice.