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It is common for people to wonder: Are DUI field sobriety tests mandatory? Another common question is: What happens if you refuse a sobriety test?

The Law Offices of Kerry L. Armstrong, APLC, has the answers and advice you are looking for.

What Are Field Sobriety Tests?

DUI field sobriety tests are exercises that police officers administer when they suspect that someone might be guilty of driving under the influence.

The tests measure a person’s ability to follow instructions while completing physical tasks.

They give officers clues about someone’s inebriation level by testing balance and coordination, while also allowing the officer to interact with the person and witness their overall demeanor and appearance. 

Types of Field Sobriety Tests

Police officers use many different field sobriety tests in California, but only three are “standardized” exercises: the Horizontal Gaze Nystagmus (HGN), the Walk-and-Turn (WAT), and the One-Leg Stand (OLS).

The National Highway Transportation Safety Administration  (NHTSA) has validated these standard tests as reliable when they are administered correctly and in proper conditions.

Horizontal Gaze Nystagmus

When someone turns their eyes to the side, at a certain point their pupil will “jerk” involuntarily. The person cannot feel this happening or control it—it is involuntary and unconscious.

This is even more true when the person has been drinking alcohol.  To perform this HGN test, the officer has the person follow something like a pen with their eyes.

The officer moves the pen to the right and left sides while instructing the subject to keep their head straight and follow the object with their eyes. The officer then notes the point at which the person’s pupils begin to jerk.

According to the NHTSA, the higher someone’s blood-alcohol content (BAC), the sooner their eye will start jerking. NHTSA claims that the test is 88% accurate for predicting BAC.


The WAT forces the person to concentrate on mental and physical tasks simultaneously.

The officer gives specific instructions for the person to take nine heel-to-toe steps in a straight line, pivot, and then take nine heel-to-toe steps back along the line.

Meanwhile, the officer watches for the person to lose their balance during instruction, start or stop too soon, fail to touch heel-to-toe, step out of line, use their arms for balance, fail to pivot correctly or take an incorrect number of steps.

According to the NHTSA, the WAT has a 79% accuracy rate.

One-Leg Stand 

The OLS also requires someone to pay attention to both mental and physical tasks.

They must raise their foot about six inches off the ground while holding still and balancing on the other leg, counting, and looking down at their foot.

The officer watches to see if the person sways, uses their arms for balance, hops, or puts their foot down. The NHTSA claims the OLS is 83% accurate.

Ideal Conditions for Testing

NHTSA requires that the tests occur under appropriate conditions for accuracy. The ground should be hard, dry, and level. There should be adequate lighting for the subject to see the officer and the ground.

They also need to be able to hear the officer. Lastly, there should be minimal distractions such as traffic or onlookers. 

Field sobriety tests in California traffic stops can also include other, non-standardized tests such as the Hand-Pat Test, the Finger-to-Nose Test, the Romberg Balance Test, and the Finger Count.

However, unlike the NHTSA tests, there is no documented correlation between the tests and someone’s impairment.

Furthermore, the administration of these tests may vary from one officer to the next.

Are You Required to Do a Field Sobriety Test?

Field sobriety tests in California are NOT mandatory. You are not breaking a law if you refuse to do these tests. 

What Happens If You Refuse a Field Sobriety Test?

Refusal will not stop an officer from arresting you. The truth is, the officer most likely already made the decision to do so before they asked you to step out of your car.

The officer already made an assessment based on your driving, appearance, quality of speech, and alcohol smell.

The test is just another tool for an officer to justify a DUI arrest, and usually only strengthens the prosecution’s case against you for a DUI conviction. 

In almost all cases you should politely refuse to perform any of the requested field sobriety tests.  

Do Not Refuse a Chemical Test

Though you can legally refuse the field sobriety tests, under California law, you cannot refuse a chemical test after arrest.

You must submit to a blood, breath, or urine test. Consequences for refusing to take a chemical test include loss of license for a year, possibly two days in jail, and an extra six months of DUI school for a first offense.

Penalties increase for subsequent offenses. 

What to Do If You are Pulled Over

If an officer pulls you over for a traffic violation, remain polite and cooperative.

You must give your identification, registration, and insurance information and step out of the car if asked.

If the officer asks you to do the field sobriety tests, you may refuse, but do so politely. You can also refuse the preliminary breath test if you are over 21.

You should also not answer any questions beyond your name—you have the right not to incriminate yourself.

Anything you say or do from the time they pull you over could be used against you in court. 

What if You Were Already Arrested for DUI and You Did the Tests?

Even if you already did the tests, your attorney may still be able to strategize a defense for your case after they read the police report.

Possible defenses to poor performance on field sobriety exercises include:

  • Your physical and mental conditions—Including illness, advanced age, injuries, balance issues, if you are overweight, brain damage, etc.;
  • Unsuitable attire—For instance, if you were wearing high-heels, tight shoes, tight pants, baggy pants, etc.;
  • Unfavorable environmental conditions—Including bad weather, bad lighting, unfavorable road conditions, or distractions;
  • Extraneous reasons for lack of physical coordination—These can include prescription medications, lack of sleep, exhaustion, dehydration, muscle fatigue, etc.;
  • Non-standardized tests performed; and
  • Improper test administration—There are many rules that officers must follow to accurately administer these tests. Failing to properly administer the test can negate the result.

For these reasons, it is important to hire an experienced attorney to handle your case as soon as possible.

An inexperienced attorney may not realize that these defenses are options, or may not be able to find the holes in the officer’s report.

The Law Offices of Kerry L. Armstrong, APLC, Is the Experienced Firm You Need 

A DUI conviction can leave you with large fines, suspended driving privileges, and jail time. DUI trials are complicated, with a lot of moving parts.

If you were arrested in California for driving under the influence, you need to hire the right attorney to protect your rights and freedoms.

Our attorneys understand the ins and outs of DUI trials and California DUI laws.

Contact the Law Offices of Kerry L. Armstrong, APLC, to schedule your consultation.

Author Photo

Kerry L. Armstrong


Attorney Kerry Armstrong opened up his law firm in June 2007. Mr. Armstrong attended Thomas Jefferson School of Law, San Diego, California, and received his B.S. from Middle Tennessee State University. Kerry L. Armstrong became certified by the State Bar of California’s Board of Legal Specialization for criminal law in August 2020, making him one of the few criminal defense attorneys with a criminal law legal specialization certificate in San Diego County.  Between 2014 – 2019, Mr. Armstrong was selected for inclusion in the California Super Lawyers list, an honor only awarded to 5% of the nation’s attorneys.

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