California DUI Field Sobriety Tests — Your Rights and How to Challenge Them

You're pulled over on I-5 near the Gaslamp Quarter at 11 p.m. The officer smells alcohol and asks you to step out of the car. What happens next — and what you do — can determine whether you face a DUI conviction under California Vehicle Code §23152 or walk away.

Field sobriety tests (FSTs) are the roadside exercises officers use to build probable cause for a DUI arrest. They feel like pass/fail tests, but they are not. They are designed to generate clues of impairment, and those clues are routinely challenged and excluded by experienced San Diego DUI defense attorneys. This guide explains how FSTs work, what your rights are, and how skilled defense lawyers attack the results.

What Is a Field Sobriety Test?

A field sobriety test is a physical or cognitive task performed at the roadside that an officer uses to evaluate whether a driver may be impaired. The National Highway Traffic Safety Administration (NHTSA) has standardized three tests — known collectively as the Standardized Field Sobriety Tests (SFSTs) — that are the most widely used and most frequently admitted in California courts:

• Horizontal Gaze Nystagmus (HGN) — The officer tracks involuntary jerking of the eye
• Walk-and-Turn (WAT) — A divided-attention test involving heel-to-toe walking and turning
• One-Leg Stand (OLS) — Balance and counting while standing on one foot for 30 seconds

Officers may also administer non-standardized tests such as the Rhomberg balance test (eyes closed, head back, estimate 30 seconds), finger-to-nose, alphabet recitation, and counting backwards. These non-standardized tests have weaker scientific support and are more easily challenged in court.

Are Field Sobriety Tests Mandatory in California?

This is the most important thing to know: for drivers age 21 and older who are not on DUI probation, field sobriety tests are voluntary. You may politely decline to perform them without any automatic legal penalty or mandatory license suspension.

California law also recognizes a Preliminary Alcohol Screening (PAS) device — the small handheld breathalyzer an officer may produce at the roadside. Under Vehicle Code §23612(h), the officer must advise you that this pre-arrest PAS test is voluntary (unless you are under 21 or on DUI probation). Many drivers do not realize they can decline it.

That said, declining FSTs is not a magic bullet. An officer can still arrest you based on other observations — the odor of alcohol, bloodshot eyes, slurred speech, driving pattern, and open containers. The decision whether to perform FSTs involves weighing several factors, and a San Diego DUI attorney can walk you through those considerations if you call before deciding (though you may not always have that luxury roadside).

The Three NHTSA Standardized Tests in Detail

1. Horizontal Gaze Nystagmus (HGN)

Nystagmus is the involuntary jerking of the eye that occurs naturally when the eye moves to extreme angles. Alcohol consumption causes this jerking to begin at less extreme angles and become more pronounced. During HGN, the officer holds a pen or flashlight about 12–15 inches from your face and moves it slowly side to side while watching your eyes.

The officer looks for six clues (three per eye):

• Lack of smooth pursuit (the eye jerks rather than follows smoothly)
• Distinct and sustained nystagmus at maximum deviation
• Onset of nystagmus prior to 45 degrees

NHTSA research estimates that four or more clues indicate a BAC of 0.08% or higher with approximately 88% accuracy when administered correctly. That means roughly 12% of sober people with four clues would be falsely identified. And that accuracy figure assumes perfect administration — which rarely happens roadside at 11 p.m. on a San Diego freeway shoulder.

2. Walk-and-Turn (WAT)

The walk-and-turn is a divided-attention test: you must listen to instructions while maintaining a heel-to-toe stance, then walk nine steps heel-to-toe along a real or imaginary line, pivot on one foot, and return nine steps. Officers look for eight clues:

• Cannot maintain balance during instructions
• Starts before instructions are finished
• Stops while walking
• Does not touch heel-to-toe
• Steps off the line
• Uses arms for balance
• Loses balance on turn or turns incorrectly
• Takes the wrong number of steps

Two or more clues are considered an indication of impairment. NHTSA estimates 79% accuracy under standardized conditions. The test requires a dry, hard, level surface with adequate lighting. A rough asphalt shoulder of Interstate 8 near Mission Valley does not meet that standard.

3. One-Leg Stand (OLS)

You stand with your feet together, arms at your sides, then raise one foot approximately six inches off the ground while counting aloud ("one-thousand-one, one-thousand-two...") until told to stop (approximately 30 seconds). Officers look for four clues:

• Sways while balancing
• Uses arms for balance
• Hops
• Puts foot down

Two or more clues indicate impairment. NHTSA estimates 83% accuracy. People who are 65 or older, have back, leg, or inner ear problems, or are 50 or more pounds overweight may have difficulty regardless of sobriety. The test is officially not validated for those populations.

The PAS Device — Roadside Breath Testing

The Preliminary Alcohol Screening device is a small, handheld breathalyzer carried by most San Diego Police Department and CHP officers. It provides a quick BAC estimate but is not the evidentiary-grade Draeger Alcotest or Intoxilyzer 8000 used back at the station or jail.

PAS devices are subject to margin-of-error arguments, calibration issues, mouth alcohol contamination, and radio frequency interference. San Diego DUI attorneys regularly request calibration records and operator certification logs for PAS devices.

How San Diego DUI Defense Attorneys Challenge FST Results

Even if you performed poorly on every FST, a skilled defense attorney has multiple avenues to challenge the evidence before it reaches a jury.

1. Improper Administration

NHTSA has published precise protocols for each SFST. The officer must demonstrate the test, give specific verbal instructions, use proper stimulus distance and movement speed for HGN, and use an appropriate surface for the WAT and OLS. Deviation from these protocols can be argued to render the results unreliable. Officers are trained on these protocols, but training and execution at 2 a.m. on a dark roadside often diverge.

2. Medical and Physical Conditions

A wide range of conditions can mimic intoxication clues:

• HGN: Inner ear disorders (labyrinthitis, Meniere's disease), neurological conditions, certain anticonvulsant medications, and high doses of aspirin can cause nystagmus in sober individuals
• WAT & OLS: Knee, hip, ankle, or back injuries; peripheral neuropathy; vertigo; and footwear (heels, flip-flops, cowboy boots) affect balance performance
• PAS/Breath Tests: GERD (acid reflux), diabetes-related ketosis producing acetone on the breath, and dentures or dental work can affect breath test readings

Defense attorneys frequently retain medical experts to explain these alternative causes to a jury or San Diego Superior Court judge.

3. Environmental Conditions

NHTSA validation studies were conducted under controlled conditions. San Diego's actual roadside conditions include:

• Uneven or sloped pavement
• Headlights, passing traffic, and nighttime darkness
• Wind and noise affecting the ability to hear instructions clearly
• Heat stress — particularly in San Diego's inland valleys during summer

Each of these factors can independently produce FST clues in sober people.

4. Motion to Suppress — Penal Code §1538.5

If the initial traffic stop was unconstitutional — the officer lacked reasonable suspicion to pull you over — all evidence gathered afterward, including FST results and chemical tests, may be suppressed under Penal Code §1538.5. Common suppression arguments in San Diego DUI cases include:

• The lane change or equipment violation that prompted the stop was not actually unlawful
• The checkpoint where you were stopped did not comply with California checkpoint requirements (Ingersoll v. Palmer, 43 Cal. 3d 1321)
• The expansion of a traffic stop into a DUI investigation was not supported by independent reasonable suspicion

A successful §1538.5 motion can result in complete dismissal of the DUI charges, even when the driver's actual BAC exceeded 0.08%.

5. Attacking the Officer's Training and Subjectivity

FST "clues" are subjective. The officer decides whether your eye movement is smooth, whether you swayed, whether your heel missed your toe. Defense attorneys cross-examine officers on their NHTSA certification, the date of their last recertification training, whether dashcam or bodycam footage contradicts their observations, and whether they documented the specific clues contemporaneously in their report or filled them in later.

DUI Penalties in California — What's at Stake

These figures exclude DUI school costs ($500–$3,000 depending on program length), SR-22 insurance surcharges, ignition interlock device installation and monitoring costs, and the collateral consequences of a DUI conviction — including professional license issues, immigration consequences, and employment background checks.

San Diego DUI Cases — Local Context

San Diego County DUI cases are prosecuted in multiple courthouses depending on where the arrest occurred: the downtown San Diego Hall of Justice (330 W. Broadway), El Cajon Superior Court for East County arrests, Vista Superior Court for North County, and South Bay (Chula Vista) for arrests near the I-805/SR-54 corridor.

San Diego has aggressive DUI enforcement. The San Diego Police Department operates regular DUI saturation patrols, particularly in the Gaslamp Quarter, Pacific Beach, Mission Valley near Qualcomm/Snapdragon Stadium events, and on I-15 and SR-163. California Highway Patrol regularly operates DUI checkpoints on major corridors. The San Diego County District Attorney's office generally does not dismiss first-time DUI cases without a compelling legal or factual defense, which makes having an experienced local attorney critical.

San Diego DUI defense attorneys also practice extensively before the San Diego DMV Driver Safety Office, which handles APS hearings separately from the criminal court process. Winning the DMV hearing — or setting aside the suspension — can allow you to continue driving even while the criminal case is pending.

Should You Refuse Field Sobriety Tests?

The answer depends on the specific circumstances, and there is no one-size-fits-all rule. Consider these factors:

• If you have had nothing to drink, performing tests that are heavily documented on bodycam may actually help your case
• If you have consumed alcohol, every FST clue recorded becomes potential trial evidence — and declining gives the prosecutor one less piece of physical evidence
• If you have a medical condition that will affect your performance independent of alcohol, disclosing this to the officer upfront (and in writing if possible) provides context that a defense attorney can use later
• Regardless of what you decide, remain polite and do not make statements about how much you have had to drink

Under the Fifth Amendment (incorporated through California Constitution Article I, §15), you have the right to remain silent. You are not required to answer questions about where you have been, what you were drinking, or when your last drink was. Politely invoking this right — "I prefer not to answer questions without my attorney present" — cannot be used as evidence of guilt.

Frequently Asked Questions