If a California police officer suspects that a driver is under the influence of alcohol, the officer may conduct several roadside tests as part of the DUI investigation. Two commonly discussed procedures are field sobriety tests (FSTs) and preliminary alcohol screening (PAS) tests.
Although these terms are sometimes used as if they describe completely separate procedures, California law treats a PAS test as a type of field sobriety test. The practical difference is that traditional field sobriety exercises involve an officer observing a person’s physical and mental performance, while a PAS test uses a breath sample to screen for alcohol.
Understanding the difference between an FST and PAS test in California can help explain what these tests are designed to show, how they may be used during a DUI investigation, and why neither test should automatically be viewed as proof of guilt.
What Is a Field Sobriety Test in California?
A field sobriety test (FST) is a roadside procedure used by law enforcement to look for signs that may be consistent with impairment.
When people refer to field sobriety tests, they are often talking about the three Standardized Field Sobriety Tests (SFSTs):
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Horizontal Gaze Nystagmus (HGN): The officer observes the person’s eye movements while the person follows a stimulus.
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Walk-and-Turn: The person is asked to take a series of steps, turn as instructed, and walk back.
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One-Leg Stand: The person is asked to stand on one leg while following specific instructions.
These exercises do not directly measure a person’s blood alcohol concentration (BAC). Instead, they allow the officer to observe physical coordination, balance, divided attention, eye movements, and the ability to follow instructions.
Officers may also use other roadside exercises during a DUI investigation. Not every exercise used by an officer is necessarily one of the three standardized SFSTs.
What Is a PAS Test in California?
PAS stands for Preliminary Alcohol Screening.
A PAS test generally requires a driver to provide a breath sample into a handheld alcohol-screening device. The device produces a reading intended to indicate the presence and approximate concentration of alcohol in the person’s breath.
The PAS is used as an investigative tool during a DUI investigation.
This is different from a post-arrest chemical test. A PAS test may occur before an arrest, while a chemical breath or blood test may be required after a lawful DUI arrest under California’s applicable testing laws.
Is a PAS Test a Field Sobriety Test?
Yes.
This is an important point when discussing California DUI law.
California law defines a preliminary alcohol screening test as a type of field sobriety test. Therefore, it is technically incorrect to say that a PAS test and a field sobriety test are completely separate categories.
However, the terms are commonly used differently in everyday conversation.
When someone says “field sobriety test,” they often mean physical roadside exercises such as the Walk-and-Turn or One-Leg Stand.
When someone says “PAS test,” they generally mean the handheld breath test used to screen for alcohol.
So, the more useful comparison is:
Physical field sobriety exercises vs. a preliminary alcohol screening breath test.
Field Sobriety Test vs. PAS Test: Key Differences
The main difference is what the officer is evaluating.
| Field Sobriety Exercises | PAS Test |
|---|---|
| Officer observes the person’s performance | Device analyzes a breath sample |
| Focuses on physical and divided-attention abilities | Focuses on alcohol in the person’s breath |
| Includes exercises such as Walk-and-Turn and One-Leg Stand | Uses a handheld alcohol-screening device |
| Does not directly measure BAC | Produces an alcohol-related reading |
| Performance can be affected by physical and environmental conditions | Results can depend on the device, testing procedures, and circumstances |
| Used as part of the overall DUI investigation | Used as an investigative alcohol-screening tool |
An officer may use both during the same traffic stop because they provide different types of information.
Why Do Police Use Field Sobriety Tests and PAS Tests?
A DUI investigation may involve several observations rather than relying on one test.
For example, an officer may first observe a driver having difficulty maintaining a lane. During the traffic stop, the officer may notice an odor of alcohol or other signs that lead to further investigation.
The officer may then:
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Ask the driver questions.
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Conduct field sobriety exercises.
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Request a PAS breath sample.
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Consider the information gathered during the investigation.
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Decide whether there is sufficient basis for an arrest.
The FST and PAS provide different information.
The field sobriety exercises allow the officer to observe the driver’s performance. The PAS provides an alcohol-related breath reading.
Does a Field Sobriety Test Measure BAC?
No.
Standardized field sobriety exercises do not directly measure blood alcohol concentration.
For example, the Walk-and-Turn does not tell an officer that a driver has a particular BAC. Instead, the officer evaluates the driver’s performance according to the exercise and records observations that may be considered as part of the DUI investigation.
Similarly, the One-Leg Stand does not produce a BAC number.
A PAS test is different because it produces an alcohol-related reading from a breath sample.
Does a PAS Test Measure BAC?
A PAS device provides a breath alcohol measurement intended to estimate alcohol concentration. However, a roadside PAS test should not automatically be treated as identical to the evidentiary chemical testing that may occur after arrest.
The purpose and circumstances of the testing are different.
A PAS is generally used during the investigative stage to help an officer evaluate whether alcohol may be involved.
After a lawful DUI arrest, a driver may be required to submit to a separate chemical test under California’s implied-consent laws.
Is a PAS Test the Same as a Breathalyzer?
Not necessarily.
“Breathalyzer” is commonly used as a general term for breath alcohol testing devices. However, a PAS device is specifically used for preliminary alcohol screening.
The important distinction in a California DUI case is whether the device was being used as a preliminary screening tool or as part of a post-arrest evidentiary chemical-testing procedure.
These procedures can involve different devices, requirements, and legal considerations.
Can a PAS Result Be Used in a California DUI Case?
A PAS result can potentially become evidence in a California DUI case.
The fact that the test is called “preliminary” does not mean its result can never be considered in court.
However, a PAS reading does not automatically establish every element of a DUI offense. The significance of the result can depend on the circumstances surrounding the test, including how it was administered and other applicable evidentiary requirements.
A DUI case may also involve other evidence, such as driving behavior, officer observations, statements, field sobriety performance, and post-arrest chemical testing.
Can Field Sobriety Tests Be Used as Evidence?
Yes.
An officer’s observations during field sobriety exercises may become part of the evidence in a DUI case.
For example, an officer may testify about:
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The instructions given to the driver
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How the driver performed the exercise
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Specific behaviors observed
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Road and weather conditions
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The driver’s footwear or other relevant circumstances
However, poor performance on a field sobriety exercise does not automatically prove that a person was driving under the influence.
The circumstances surrounding the exercise can matter.
What Can Affect Field Sobriety Test Performance?
Field sobriety exercises are conducted on the roadside rather than in controlled conditions.
Performance can potentially be affected by factors such as:
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Uneven pavement
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Poor lighting
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Weather conditions
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Traffic or other distractions
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Footwear
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Physical limitations
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Balance or coordination problems
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Difficulty hearing or understanding instructions
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Nervousness
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The way the exercise was administered
These circumstances may be relevant when evaluating an officer’s observations.
For example, a driver performing the One-Leg Stand on an uneven surface may have difficulty maintaining balance for reasons unrelated to alcohol.
What Can Affect a PAS Test Result?
PAS testing also involves specific equipment and procedures.
Potentially relevant circumstances may include:
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The type of PAS device used
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Whether the device was functioning properly
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How the test was administered
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Whether applicable procedures were followed
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The timing of the test
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Circumstances surrounding the breath sample
A PAS reading should therefore be considered in the context of the entire DUI investigation rather than automatically treated as conclusive proof of impairment.
Can You Refuse a Field Sobriety Test in California?
The legal consequences of declining a roadside field sobriety exercise are different from the consequences associated with refusing a required post-arrest chemical test.
California’s implied-consent rules primarily concern chemical testing after a lawful DUI arrest. They should not simply be treated as applying in the same way to every roadside exercise.
PAS testing also has specific rules, including special requirements that can apply to certain drivers, such as drivers under 21 or drivers on DUI probation.
Because the legal consequences can vary depending on the circumstances, it is important not to assume that refusing one type of test has the same consequences as refusing another.
Is Refusing a PAS Test the Same as Refusing a Chemical Test?
No.
A PAS test and a post-arrest chemical test are different procedures.
The PAS is generally used as a preliminary investigative tool.
A post-arrest chemical test is conducted under California’s chemical-testing and implied-consent laws.
This distinction is particularly important because refusal of a required post-arrest chemical test can result in separate legal and DMV consequences.
Does Passing a Field Sobriety Test Mean You Cannot Be Arrested?
No.
Field sobriety tests are only one part of a DUI investigation.
An officer may consider other information, including:
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Driving behavior
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Statements
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Physical observations
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Field sobriety performance
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PAS results
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Other evidence obtained during the investigation
Likewise, performing poorly on a field sobriety exercise does not automatically establish guilt.
The overall circumstances of the investigation matter.
Does a PAS Result Automatically Mean You Will Be Charged With DUI?
No.
A PAS result is one piece of evidence that may be considered during a DUI investigation.
California DUI law includes separate offenses involving driving while under the influence and driving with a BAC at or above the applicable legal threshold. The evidence in a particular case can therefore involve more than a single roadside breath reading.
For example, an officer may consider the PAS result together with driving behavior, field sobriety performance, physical observations, and other evidence.
Example: FST and PAS During the Same DUI Stop
Consider a hypothetical example.
A police officer stops a driver after observing the vehicle drifting within its lane.
During the conversation, the officer reports an odor of alcohol and notices that the driver appears to have difficulty following instructions.
The officer conducts the Walk-and-Turn and One-Leg Stand.
The driver has difficulty with portions of the exercises.
The officer then administers a PAS test, which produces an alcohol-related reading.
The officer may consider all of these observations together when determining whether to make an arrest.
The example demonstrates the different roles of the tests:
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Field sobriety exercises: Provide observations about the driver’s performance.
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PAS: Provides an alcohol-related breath reading.
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Other observations: Provide additional context for the investigation.
The PAS does not replace the field sobriety exercises, and the field sobriety exercises do not replace chemical testing that may be required after arrest.
Frequently Asked Questions
What is the difference between an FST and PAS test?
A PAS is technically a type of field sobriety test under California law. However, “FST” is commonly used to refer to physical or divided-attention exercises such as the Walk-and-Turn and One-Leg Stand, while a PAS involves a breath sample used to screen for alcohol.
What are the three standardized field sobriety tests?
The three standardized tests are the Horizontal Gaze Nystagmus, Walk-and-Turn, and One-Leg Stand.
Does an FST measure BAC?
No. Standardized field sobriety exercises evaluate a person’s performance and do not directly measure BAC.
Does a PAS test measure alcohol?
Yes. A PAS device analyzes a breath sample and provides an alcohol-related reading.
Is a PAS the same as a post-arrest breath test?
No. A PAS is a preliminary investigative test. A post-arrest chemical breath test is a separate procedure governed by California’s applicable chemical-testing laws.
Can a PAS result be used in court?
A PAS result can potentially be admitted or considered as evidence, depending on the circumstances and applicable evidentiary requirements.
Does failing an FST prove DUI?
No. Field sobriety performance is one type of evidence that may be considered during a DUI investigation. It does not automatically establish guilt.
Does passing an FST prevent an arrest?
No. An officer may consider other evidence and observations when determining whether there is sufficient basis for an arrest.
Can you refuse a PAS test in California?
The answer can depend on the driver’s circumstances. California has different rules for certain categories of drivers, including drivers under 21 and drivers on DUI probation. PAS testing should also be distinguished from post-arrest chemical testing.
Key Takeaway
The terminology surrounding California DUI testing can be confusing because a PAS test is technically a type of field sobriety test.
In practical terms, however, the distinction is straightforward:
Field sobriety exercises involve an officer observing physical and divided-attention performance, while a PAS test uses a breath sample to screen for alcohol.
The two procedures may be used during the same DUI investigation because they provide different information.
A field sobriety exercise does not directly measure BAC, while a PAS produces an alcohol-related breath reading. Neither procedure automatically determines guilt, and a PAS is not necessarily the same as the post-arrest chemical test that may follow a DUI arrest.
Understanding what each test is designed to do—and what it does not establish—can provide a clearer picture of how a California DUI investigation works.
Contact Southwest Legal
Have Questions About a California DUI Investigation?
If you are dealing with a California DUI arrest or investigation, questions about field sobriety tests, PAS results, and chemical testing can be confusing. The circumstances surrounding each test may matter when understanding the legal issues involved.
Southwest Legal can help you better understand the DUI process and the issues that may arise in your case. For answers tailored to your circumstances, contact us today for a free consultation.
Disclaimer: This article is for general informational purposes only and does not constitute legal advice or create an attorney-client relationship unless and until the firm and client enter into an agreement for legal services. Laws may change, and legal outcomes depend on the specific facts of each case. Consult a qualified attorney for advice regarding your situation.