DUI Field Sobriety Tests in Arizona

The Tests Police Use Against You Are Not as Reliable as They Claim

When an officer pulls you over and suspects impairment, the first tool in their arsenal is the field sobriety test. These roadside tests are presented as scientific instruments of detection. The officer will describe them as simple tasks that any sober person can perform. The prosecution will present the results as objective evidence of impairment.

The reality is different. Field sobriety tests are subjective, poorly administered, affected by dozens of non-alcohol factors, and far less reliable than the public has been led to believe. Even the National Highway Traffic Safety Administration (NHTSA), the federal agency that developed and standardized these tests, acknowledges significant error rates.

Brad Rideout is a former Arizona District Attorney who used field sobriety test evidence to prosecute DUI cases for years. He knows how prosecutors present this evidence, how they train officers to testify about it, and how they downplay the limitations. Now he uses that inside knowledge to challenge field sobriety test evidence from the defense side – exposing the weaknesses that prosecutors prefer to keep hidden.

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Field Sobriety Tests Are Voluntary in Arizona

This is the single most important fact about field sobriety tests: you are not required to take them.

Arizona law does not require drivers to perform field sobriety tests. There is no penalty for refusing. You will not lose your license for declining. You will not be charged with an additional crime for saying no.

The implied consent law under A.R.S. § 28-1321 applies to chemical testing (blood and breath) after arrest – not to pre-arrest field sobriety tests. Officers may tell you the tests are “just to make sure you’re okay to drive” or that “cooperating will help your case.” Neither statement is accurate. The tests exist for one purpose: to build probable cause for your arrest and to generate evidence for the prosecution.

If you are reading this page before a DUI encounter, remember this: politely decline field sobriety tests. You are not helping yourself by performing them. You are providing the prosecution with evidence.

If you have already taken the tests and been arrested, the results can still be challenged. That is where experienced defense representation matters.

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The Three Standardized Field Sobriety Tests

NHTSA developed and validated three Standardized Field Sobriety Tests (SFSTs) through research conducted in the late 1970s and 1980s. These are the only field sobriety tests that NHTSA considers scientifically validated, and they are the three tests most commonly administered by Arizona law enforcement:

1. Horizontal Gaze Nystagmus (HGN)

What It Is

Nystagmus is an involuntary jerking or bouncing of the eye. Horizontal gaze nystagmus refers to the jerking that occurs when the eyes track an object moving horizontally across the field of vision. Alcohol and certain other substances can cause this nystagmus to become more pronounced and to occur at earlier angles of gaze.

During the HGN test, the officer holds a stimulus (typically a pen, penlight, or finger) approximately 12 to 15 inches from your face and moves it slowly from side to side. The officer watches your eyes for three specific indicators in each eye, for a total of six possible “clues”:

1. Lack of smooth pursuit – Does the eye jerk or bounce as it tracks the stimulus, rather than following smoothly?
2. Distinct and sustained nystagmus at maximum deviation – When the eye is held at the farthest point to one side, does it exhibit visible jerking for at least four seconds?
3. Onset of nystagmus prior to 45 degrees – Does the jerking begin before the eye has moved 45 degrees from center?

According to NHTSA, the presence of four or more clues (out of six) indicates a BAC of 0.08 or above. NHTSA claims the HGN test is 77% accurate at identifying drivers above 0.08 BAC.

Why the HGN Test Is Unreliable

The 77% accuracy claim means that 23% of the time, the test incorrectly identifies a sober driver as impaired. That is nearly one in four.

Beyond the baseline unreliability, the HGN test is affected by numerous factors unrelated to alcohol consumption:

• Medical conditions – Brain stem lesions, inner ear disorders, multiple sclerosis, and other neurological conditions can cause nystagmus
• Medications – Anti-seizure drugs, anti-depressants, barbiturates, and many prescription medications cause nystagmus
• Eye conditions – Lazy eye, prior eye surgery, cataracts, and natural nystagmus (present in a percentage of the population)
• Fatigue – Extreme tiredness can produce nystagmus-like eye movements
• Caffeine and nicotine – Both can affect eye tracking
• Flashing lights – Police emergency lights and passing traffic can produce optokinetic nystagmus that mimics alcohol-induced nystagmus
• Administration errors – The officer must hold the stimulus at the correct distance, move it at the correct speed, and hold it at maximum deviation for the correct duration. Deviations from the standardized protocol invalidate the results

Officers receive limited training on the HGN test – typically a few hours during the SFST training course. They are not ophthalmologists or neurologists. Their ability to distinguish alcohol-induced nystagmus from other causes is limited.

2. Walk-and-Turn Test

What It Is

The walk-and-turn test is a “divided attention” test designed to require the subject to perform physical tasks while following verbal instructions simultaneously. The theory is that alcohol impairs the ability to divide attention between mental and physical tasks.

The test requires you to:

1. Stand in a heel-to-toe position with your arms at your sides while the officer explains the test (the “instruction phase”)
2. Take nine heel-to-toe steps along a straight line
3. Turn in a specific manner (small steps, keeping one foot on the line)
4. Take nine heel-to-toe steps back

The officer watches for eight possible clues:

1. Cannot keep balance during instructions
2. Starts too soon
3. Stops while walking
4. Does not touch heel to toe
5. Steps off the line
6. Uses arms for balance (raises arms more than 6 inches from sides)
7. Improper turn
8. Wrong number of steps

Two or more clues indicate impairment, according to NHTSA. NHTSA claims the walk-and-turn test is 68% accurate at identifying drivers above 0.08 BAC.

Why the Walk-and-Turn Test Is Unreliable

A 68% accuracy rate means the test is wrong nearly one-third of the time. If you used a medical test with a 32% error rate, you would demand a second opinion.

The walk-and-turn test is profoundly affected by non-alcohol factors:

• Age – People over 65 have difficulty performing heel-to-toe walking regardless of sobriety
• Weight – Individuals who are 50 or more pounds overweight face balance challenges unrelated to impairment
• Footwear – High heels, boots, sandals, and platform shoes significantly affect balance. Officers are supposed to offer the option to remove shoes, but many do not
• Road surface – Gravel, slopes, cracked pavement, grass, and wet surfaces make the test more difficult. NHTSA requires a “dry, hard, level, non-slippery surface,” but many DUI stops occur on road shoulders that do not meet this standard
• Physical conditions – Back injuries, knee problems, hip replacements, inner ear disorders, leg injuries, and neurological conditions all affect performance
• Weather – Wind, rain, cold, and heat affect balance and concentration
• Nervousness – The stress of a roadside encounter with law enforcement causes anxiety that affects coordination and the ability to follow instructions
• Lighting – Many DUI stops occur at night. Poor lighting makes it difficult to see the line you are supposed to walk on
• Officer instructions – If the officer gives unclear or incomplete instructions, the subject may perform the test incorrectly not because of impairment but because of confusion

The NHTSA SFST Manual itself acknowledges that the test should not be administered to individuals over 65, more than 50 pounds overweight, or with physical impairments affecting balance. Yet officers routinely administer the test to people in all of these categories and then testify that their poor performance indicates impairment.

3. One-Leg Stand Test

What It Is

The one-leg stand test requires you to stand on one foot with the other foot raised approximately six inches off the ground, toes pointed forward, while counting out loud (“one thousand one, one thousand two…”) for 30 seconds.

The officer watches for four clues:

1. Swaying while balancing
2. Using arms for balance (raising arms more than 6 inches)
3. Hopping to maintain balance
4. Putting the raised foot down

Two or more clues indicate impairment. NHTSA claims the one-leg stand test is 65% accurate at identifying drivers above 0.08 BAC.

Why the One-Leg Stand Test Is Unreliable

A 65% accuracy rate is barely better than a coin flip. Yet this test is presented in courtrooms as scientific evidence of impairment.

The same non-alcohol factors that affect the walk-and-turn test apply here with even greater force:

• Standing on one foot for 30 seconds is difficult for many completely sober people, particularly those over 50, overweight, or with any lower body joint issue
• Uneven surfaces, wind, and poor lighting compound the difficulty
• The anxiety of a police encounter causes muscle tension and trembling that mimics swaying
• Officers frequently fail to time the test accurately, asking subjects to hold the position for longer than 30 seconds
• Footwear, road conditions, and weather are rarely documented in the officer’s report

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Non-Standardized Field Sobriety Tests

Some officers administer additional tests that are not part of the NHTSA standardized battery. These include:

• Finger-to-nose test – Touching the tip of your nose with your index finger while your eyes are closed
• Alphabet test – Reciting a portion of the alphabet (typically not A through Z)
• Counting test – Counting backward from a specified number
• Romberg balance test – Standing with feet together, head back, eyes closed, estimating 30 seconds
• Finger dexterity test – Touching your thumb to each finger in sequence

None of these tests have been validated by NHTSA. They have no established accuracy rates. They have no standardized administration protocols. They are essentially the officer’s personal assessment of your coordination, and they carry no more scientific weight than the officer’s opinion.

Despite this, prosecutors routinely introduce non-standardized test results as evidence of impairment. Challenging the admission of this evidence is a critical part of DUI defense.

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How Officers Are Trained (And Where Training Falls Short)

The NHTSA SFST Student Manual is the standard training resource for field sobriety test administration. Officers typically complete a 24-hour SFST training course that covers the three standardized tests, their administration protocols, and clue identification.

Twenty-four hours. That is the total training an officer receives before they are certified to administer tests that will be used as the primary evidence to charge you with a crime.

The NHTSA manual is specific about administration requirements:

• The HGN stimulus must be held 12-15 inches from the subject’s face
• The stimulus must be moved at a specific speed (approximately 2 seconds per pass)
• The walk-and-turn test must be conducted on a dry, hard, level, non-slippery surface
• Each test must be administered in a specific sequence with specific verbal instructions
• The officer must demonstrate the tests before the subject performs them

In practice, officers frequently deviate from these requirements. They administer tests on sloped road shoulders, in poorly lit areas, next to busy highways with flashing lights, and in extreme weather. They skip demonstrations. They give incomplete instructions. They fail to ask about medical conditions or physical limitations. They do not account for the subject’s age, weight, or footwear.

Every deviation from the standardized protocol undermines the validity of the results. The NHTSA manual itself states that the tests are valid only when administered according to standardized procedures. Deviate from the protocol, and the claimed accuracy rates no longer apply.

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Body Camera Evidence – The Defense’s Best Tool

Arizona law enforcement body cameras have transformed DUI defense. Before body cameras, the officer’s report was the only record of the field sobriety test encounter. The report was written after the fact, from the officer’s perspective, emphasizing evidence of impairment and minimizing evidence of sobriety.

Body camera footage provides an objective record. And that record frequently contradicts the officer’s written report.

Common discrepancies revealed by body camera footage:

• The subject performed better than the report suggests. Officers document clues of impairment but often fail to document signs of sobriety. Body camera footage may show the subject walking a straight line for eight out of nine steps, using arms for balance only slightly, or standing on one leg for 25 out of 30 seconds. The report will emphasize the failures while the video shows substantial compliance.
• The officer deviated from the standardized protocol. The camera captures the officer’s actual instructions, demonstrations (or lack thereof), and test administration. If the officer gave unclear instructions or failed to demonstrate the tests properly, the video proves it.
• Environmental conditions were worse than reported. The camera shows the road surface, weather conditions, lighting, traffic, and other environmental factors that affected performance. Officers rarely document these conditions in detail in their reports.
• The officer’s demeanor was intimidating. Some officers are confrontational during field sobriety test administration, which increases anxiety and affects performance. The camera captures the officer’s tone, body language, and proximity.

Brad Rideout, as a former prosecutor, knows how to use body camera footage to dismantle field sobriety test evidence. He knows what prosecutors expect the footage to show, and he knows how to identify the moments where the officer’s conduct or the subject’s performance undermines the prosecution’s narrative.

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Challenging Field Sobriety Test Evidence in Court

Field sobriety test results are not automatic proof of impairment. They are evidence that can be challenged, rebutted, and excluded. Effective defense strategies include:

Suppression Motions

If the officer lacked reasonable suspicion for the traffic stop or probable cause for the arrest, all evidence obtained as a result – including field sobriety test results – may be suppressed. Without this evidence, the prosecution’s case often cannot proceed.

Expert Testimony

Defense experts in standardized field sobriety testing can testify about the limitations of the tests, the significance of administration errors, the impact of non-alcohol factors, and the actual (as opposed to claimed) accuracy rates. Expert testimony educates the jury about what the tests actually prove – and what they do not.

Cross-Examination of the Officer

Officers who administer field sobriety tests are trained to testify in a particular way. As a former prosecutor, Brad Rideout trained officers to testify in DUI cases. He knows the script. He knows where the gaps are. He knows the questions that officers are not prepared to answer about test limitations, administration errors, and the significance of environmental conditions.

Medical and Physical Evidence

Documentation of medical conditions, physical limitations, medications, or other factors that could explain poor field sobriety test performance independent of alcohol impairment provides a concrete alternative explanation for the jury to consider.

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Frequently Asked Questions

Do I have to take field sobriety tests if an officer asks?

No. Field sobriety tests are voluntary in Arizona. You have the right to decline without penalty. Politely tell the officer that you respectfully decline to perform field sobriety tests. This is different from chemical testing (blood or breath), which is governed by Arizona’s implied consent law.

Will refusing field sobriety tests prevent me from being arrested?

Not necessarily. If the officer has other indicators of impairment – odor of alcohol, slurred speech, bloodshot eyes, erratic driving – they may arrest you without field sobriety test results. However, refusing the tests deprives the prosecution of a significant piece of evidence. You cannot fail a test you do not take.

Can field sobriety test results be used against me in court?

Yes. If you perform field sobriety tests, the results can be presented as evidence at trial. The officer will testify about the clues observed, and the prosecution will argue that the results demonstrate impairment. This is why declining the tests is generally advisable – it eliminates this evidence from the prosecution’s case.

What if I have a medical condition that affects my balance?

Medical conditions that affect balance, coordination, or eye movement can produce field sobriety test results that mimic impairment. If you have such a condition, document it with your physician. Your attorney can present medical evidence to explain your test performance as a result of the medical condition rather than alcohol impairment.

Does the officer have to tell me the tests are voluntary?

No. Arizona law does not require officers to inform you that field sobriety tests are voluntary. Officers typically frame the request as an instruction rather than a request. “I need you to step out of the vehicle and perform some tests” sounds like a command, not a request. But it is a request, and you have the right to decline.

What if I performed well on the tests but was still arrested?

This happens more often than most people realize. Officers sometimes arrest drivers despite reasonable performance on field sobriety tests based on other indicators. In these cases, the field sobriety test results actually become defense evidence. Body camera footage showing competent performance on the tests can undermine the prosecution’s claim of impairment.

Are non-standardized tests admissible in court?

Non-standardized field sobriety tests have not been scientifically validated by NHTSA. Their admissibility varies by jurisdiction and judge. Defense attorneys can challenge the admission of non-standardized test results based on the lack of scientific validation, the absence of standardized administration protocols, and the officer’s lack of specific training on the non-standardized test.

How does the NHTSA SFST Manual help my defense?

The NHTSA SFST Manual establishes the standardized protocol that officers must follow. When officers deviate from the manual’s requirements, the defense can cite the manual to demonstrate that the test results are invalid. The manual also documents the limitations and accuracy rates of the tests, which are often lower than jurors expect.

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A Former Prosecutor Who Knows the Playbook

Brad Rideout is a former Arizona District Attorney. He spent years using field sobriety test evidence to prosecute DUI cases. He trained officers to administer these tests and to testify about the results in court.

Now he takes that same expertise and turns it around. He knows what the prosecution’s case depends on. He knows where field sobriety test evidence is weakest. He knows the questions that expose administration errors, environmental problems, and subjective interpretation.

If you were arrested for DUI after performing field sobriety tests, those test results are a pillar of the prosecution’s case. Challenging that pillar effectively requires an attorney who understands the tests from both sides.

Contact Rideout Law Group Today

Scottsdale Office

11111 N Scottsdale Rd, Suite 225

Scottsdale, AZ 85254

Phone: (480) 584-3328

Lake Havasu City Office

2800 Sweetwater Ave A-104

Lake Havasu City, AZ 86406

Phone: (928) 854-8181

Toll-Free: (833) 854-8181

Call now for a confidential consultation. Brad Rideout will review the field sobriety test evidence in your case, identify the weaknesses, and build a defense that challenges the prosecution’s version of events.