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Understanding Field Sobriety Tests in California

Understanding Field Sobriety Tests in California: Procedures and Legal Implications

Field sobriety tests (FSTs) are a critical tool used by law enforcement in California to determine if a driver is under the influence of alcohol or drugs. These tests, administered during traffic stops, play a significant role in DUI investigations. This blog provides a comprehensive overview of field sobriety tests, detailing their procedures, the science behind them, and the legal implications for drivers. Understanding these tests, their accuracy, and your rights can help you navigate a DUI stop more effectively.

Types of Field Sobriety Tests

Field sobriety tests are designed to assess a driver's physical and cognitive abilities to determine impairment. The most common FSTs used in California include:

1. Horizontal Gaze Nystagmus (HGN) Test: This test measures the involuntary jerking of the eye as it follows a moving object, such as a pen or flashlight. An officer looks for distinct eye movements that can indicate intoxication.

2. Walk-and-Turn (WAT) Test: In this divided attention test, the driver is asked to take nine heel-to-toe steps along a straight line, turn on one foot, and return in the same manner. This test assesses balance, coordination, and the ability to follow instructions.

3. One-Leg Stand (OLS) Test: The driver must stand on one leg while counting aloud for about 30 seconds. This test evaluates balance and concentration.

Procedures for Administering Field Sobriety Tests

Field sobriety tests are typically conducted on the roadside after a traffic stop. Here is the general procedure:

1. Initial Observation: The officer observes the driver's behavior and appearance, noting signs of intoxication such as slurred speech, the smell of alcohol, or erratic driving.

2. Request to Exit Vehicle: If the officer suspects impairment, they will ask the driver to exit the vehicle and move to a safe area for testing.

3. Explanation and Demonstration: The officer explains and demonstrates each test, ensuring the driver understands the instructions.

4. Test Administration: The driver performs the tests while the officer observes and records any signs of impairment.

The Role of Field Sobriety Tests in DUI Investigations

Field sobriety tests serve as preliminary assessments to determine if there is probable cause for a DUI arrest. They are part of a broader investigative process that may include:

1. Preliminary Alcohol Screening (PAS): Following FSTs, an officer may use a breathalyzer to measure blood alcohol concentration (BAC).

2. Arrest and Chemical Testing: If the FSTs and PAS suggest impairment, the officer may arrest the driver and conduct further chemical tests (breath, blood, or urine) to confirm intoxication levels.

Legal Rights During Field Sobriety Tests

Understanding your legal rights during a DUI stop is crucial. Here are key points to consider:

1. Refusal to Participate: In California, drivers are not legally required to perform field sobriety tests. You have the right to politely decline these tests, although refusal may result in arrest based on other observations.

2. Chemical Tests: Unlike FSTs, California's implied consent law requires drivers to submit to chemical testing (breath, blood, or urine) if arrested for DUI. Refusal to take these tests can result in automatic license suspension and other penalties.

3. Legal Representation: You have the right to consult with an attorney if you are arrested for DUI. Seeking legal advice early can help protect your rights and build a strong defense.

Accuracy and Validity of Field Sobriety Tests

Field sobriety tests are not foolproof and can be influenced by various factors, including:

1. Environmental Conditions: Uneven surfaces, poor lighting, and adverse weather can affect test performance.

2. Physical and Medical Conditions: Certain medical conditions, injuries, or physical limitations can impair test performance unrelated to intoxication.

3. Officer Training and Bias: The accuracy of FSTs depends on the officer's training and objectivity. Improper administration or bias can lead to inaccurate results.

DUI Defense Strategies

If you are facing DUI charges based on field sobriety tests, several defense strategies may be employed:

1. Questioning Test Validity: Challenging the accuracy and administration of FSTs can be a strong defense. An experienced DUI attorney can examine whether the tests were conducted properly and if the results were affected by external factors.

2. Medical and Physical Explanations: Presenting evidence of medical conditions or physical limitations that could have affected test performance can help counter the prosecution's claims.

3. Procedural Errors: Any errors or violations of protocol by law enforcement during the DUI stop and testing process can be used to contest the charges.


Field sobriety tests play a crucial role in DUI investigations in California, but they are not without controversy and limitations. Understanding the procedures, legal implications, and potential inaccuracies of these tests is essential for drivers. If you face DUI charges, hiring a knowledgeable DUI defense attorney can significantly impact the outcome of your case, ensuring your rights are protected and providing you with the best possible defense.

By comprehensively understanding field sobriety tests and your legal rights, you can navigate DUI stops and charges more effectively. Stay informed and seek legal guidance when necessary to protect yourself in such challenging situations.

H Law Group Online

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