Field Sobriety Tests

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Understanding Field Sobriety Tests (FSTs) in DUI Cases

Introduction to Field Sobriety Tests

While Field Sobriety Tests are completely optional, police officers have perfected the art of getting unsuspecting drivers to perform them without knowing they have a choice. Field Sobriety Tests, or "FSTs," server two primary purposes for law enforcement: they provide the officer with probable cause to make an arrest, and they help to prove intoxication at a subsequent trial. If you've been pulled over and suspected of DUI, it's essential to understand FSTs and their implications. At The Hoyle Firm, we understand the intricacies of these tests, and most importantly how to exploit any mistakes the officer may have made administering these tests. 

What are Field Sobriety Tests (FSTs)?

Field Sobriety Tests are a series of physical and cognitive tasks that police officers administer roadside to individuals they suspect of DUI. These tests aim to identify impairment signs in a person's balance, physical ability, attention level, or other faculties that might be affected by drugs or alcohol.

Common Types of FSTs

  1. Horizontal Gaze Nystagmus (HGN) Test: This test involves an officer moving an object, like a pen or flashlight, horizontally in front of the suspect's eyes. The officer observes the eyes for involuntary jerking movements (nystagmus). Alcohol or certain drugs can exaggerate this jerking, making it more noticeable.

  2. Walk-and-Turn Test: In this test, the suspect is asked to walk heel-to-toe along a straight line, turn on one foot, and then walk back in the same manner. The officer looks for signs of impairment, such as not staying on the line, starting before instructed, or using arms to balance.

  3. One-Leg Stand Test: The suspect is instructed to stand on one foot while raising the other foot approximately six inches off the ground and counting aloud. An officer will look for signs like swaying, hopping, or putting the foot down.

Are FSTs Reliable?

While FSTs can give indications of impairment, they are not foolproof. Many factors can affect an individual's performance on these tests:

  • Medical Conditions: Conditions like vertigo, inner ear problems, or neurological issues can impact balance and eye movement, which may cause a person to "fail" even if sober.
  • Physical Limitations: Age, injury, or lack of physical fitness can hinder a person's ability to perform the tests as described.
  • Nervousness: Being pulled over by the police can be nerve-wracking, which can impact performance.
  • Environmental Factors: Uneven road surfaces, poor lighting, or inclement weather can affect a person's ability to complete the tests.

Legal Implications of FSTs

If an officer determines, based on FST performance and other observations, that a driver is impaired, they may arrest the driver for DUI. However, the subjective nature of FSTs means that their results can be challenged in court.

It's crucial to note that while drivers in many jurisdictions can refuse to undergo FSTs, there may be consequences for doing so, such as license suspension or additional charges. Always consult local laws and a knowledgeable attorney.


While Field Sobriety Tests can provide evidence of impairment, it's essential to remember their inherent limitations and potential biases. If you're facing a DUI charge based on FST results, seek expert legal representation to ensure your rights are protected. Understanding the nuances of FSTs can make a significant difference in the outcome of a DUI case. Call us today at 619-432-5808 (CA) or 480-648-3555 (AZ)

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