Law Offices of M. Gabriela Guraiib

How Do Sobriety Tests Work in California?


If you’ve ever watched a show about the police, you’re probably familiar with the idea of sobriety tests. If you’ve been pulled over while driving, you may have even taken one. Law enforcement officers use these tests to determine whether someone is too impaired to drive. 

Because they’re so well-known, many people believe sobriety tests are well-studied and reliable ways to determine if someone is intoxicated. However, that’s not always the case. There are many kinds of sobriety tests, and their effectiveness and reliability can vary dramatically. Here’s what you need to know about these tests, when you need to take them, and what to do if you’ve been charged with a DUI based on a faulty sobriety test.

Types of Sobriety Tests in California

There are two main kinds of sobriety tests used in California: field checks and chemical checks. A field test is a simple activity that police officers can ask drivers to perform without the need for extra equipment. There are many field checks frequently used by police, but they aren’t equally consistent. The National Highway Traffic Safety Administration (NHTSA) has validated and provided testing standards for the following tests:

  • Walk-and-Turn: The person must take nine heel-toe steps in a straight line, turn on the spot, then take another nine steps in the opposite direction. If they lose count, lose their balance, fail to pivot, or don’t take heel-toe steps, they are most likely intoxicated. The NHTSA has found this test to be 79% accurate when performed correctly.
  • One-Leg Stand: The person must stand on one foot while counting and looking down. If they lose count, lose their balance, or put their foot down, they are likely to be intoxicated. The NHTSA has determined this test to be 83% accurate in proper conditions.
  • Horizontal Gaze Nystagmus: The officer will hold a pen or other object in front of the person’s face and move it from side to side while the person keeps their head still. The officer is looking for nystagmus or involuntary jerking of the eye. Intoxicated people will experience nystagmus significantly sooner than sober people. Correctly performed, this test is 88% accurate.

These three activities are the only ones for which the NHTSA has provided standards. Their accuracy relies on officers being trained in how to administer them. They should be performed on hard, dry, level ground, with minimal distractions and adequate lighting. Other checks, such as counting fingers or putting your finger on your nose, are not standardized and are significantly less likely to be meaningful. 

In contrast, a chemical test analyzes a sample provided by the subject to determine if there are traces of intoxicating substances present in their system. Chemical tests are typically more accurate, but they also take effort to perform. The most common chemical options are breathalyzers and blood tests. 

In a breathalyzer test, you blow into a device that looks for trace amounts of alcohol in your breath. These tests are portable and are the most common form of chemical sobriety check. Most are only designed to check for alcohol, not other substances.

Blood tests involve having your blood drawn and analyzed. These analyses can check for various substances, including alcohol, cannabis, and illicit substances. They are less common because they require the test subject to come to the police station. 

Are Sobriety Tests Mandatory?

Only chemical sobriety tests are mandatory in California. You are required by law to agree to breathalyzer or blood tests if a law enforcement officer requests it. You can lose your driver’s license if you do not agree to take them.

In contrast, you have the right to refuse field tests. An officer can request you perform these activities but cannot require you to do so. However, if you refuse a field test, the officer will likely require you to take a breathalyzer test anyway. Furthermore, if you refuse to perform a field check, the officer may assume that you are attempting to hide your intoxication and may choose to arrest you on DUI charges anyway.

Can You Dispute Sobriety Test Results?

Yes, you can dispute specific sobriety test results. In California, field tests only provide probable cause, not an objective measure of intoxication. If you have been charged with a DUI based on field sobriety checks, you can dispute the charges on the grounds that you were not appropriately tested. 

You may also be able to contest DUI charges based on chemical tests. While chemical analyses are more reliable than field checks, they are not infallible. Mechanical issues and human error can lead to incorrect results. Reasons why a chemical sobriety test result may be inaccurate include:

  • Improperly maintained testing devices, such as miscalibration or incorrect chemical solutions
  • Incorrect administration, such as having you blow into the testing device too long
  • Faulty device programming by the manufacturer

In addition, health conditions like diabetes or acid reflux can cause breathalyzers to record a higher blood-alcohol content than you actually have. Even mouthwash can cause a breathalyzer to falsely identify you as over the legal limit.

Defend Yourself Against DUI Allegations

Sobriety tests are usually the most substantial evidence the prosecution has in DUI cases. You can contest your charges if you’ve been charged with a DUI based on a faulty field or chemical sobriety check. In many cases, successfully disputing the results of a sobriety test may lead to your charges being dropped entirely. The best way to stand up to faulty sobriety results is to work with a knowledgeable DUI attorney. At the Law Offices of M. Gabriela Guraiib, we have years of experience defending clients against Redwood City DUI charges. Reach out today to learn how we can protect you against inaccurate DUI charges.