Field Sobriety Test vs Breathalyzer: What’s the Difference?

October 22, 2019

When a police officer pulls over a suspected drunk driver, they can administer several tests to determine the sobriety of the individual. You’ve probably seen or heard of these tests: walking in a straight line, following the finger with your eyes, or even using the standard breathalyzer. But how do these tests truly determine your level of sobriety? What’s the difference between a field sobriety test vs breathalyzer? Here at Low Cost Interlock, we can be of help in most DUI cases, providing resources such as car breathalyzers, as well as general information. Read on to find out more about sobriety testing.

Standardized Sobriety Test

When an individual is pulled over for driving under the influence, the Standardized Sobriety Test is the first thing a police officer will ask you to perform before you are arrested. This test has the same questions and tasks for everyone, and most police officers are certified to use it. This test is broken up into three parts:

#1: The Horizontal Gaze Nystagmus Test

The horizontal gaze nystagmus test, or NGM test, comes first. Nystagmus is the “involuntary jerking of the eyeball that occurs when the eyes track an object that moves side to side.” When you are sober, nystagmus will happen when the eyes are rotated peripherally. When a person is intoxicated, this will occur at any angle. 

To test for this, law enforcement officers will ask you to follow their finger or pen with your eyes as they move their hand back and forth in front of you. There are three telltale signs of impairment the officer will be looking for:

  • The jerking movement is sustained
  • The eye does not move evenly
  • The jerking happens before the eye is 45 degrees off-center.

#2: The Walk-and-Turn Test 

The walk-and-turn test is when the person in question is asked to take nine heel-to-toe steps in a straight line, turn one foot, and take another nine steps back. Heel-to-toe refers to taking steps where the heel of the foot moving touches the toe of the other. An individual can fail this test for several reasons.

  • Starting before end of instructions
  • Stepping away from the line
  • Imbalance or taking a step to steady themselves
  • Not walking heel-to-toe
  • Using arms to balance
  • Taking more or less than nine steps

#3: The 1-Leg Stand Test

The 1-leg stand test works as it sounds. The person in question will be asked to hold one foot about 6 inches off the ground. The officer will have the person count out loud, starting from 1,000. They set a 30-second timer and look for a few signs that the individual is impaired.

  • Hopping to try to regain their balance
  • Putting the foot down
  • Swaying or using arms to balance
  • Forgetting what number they’re on

After the sobriety tests have been administered, next up is the breathalyzer. 


A breathalyzer is a tool that tests blood alcohol content to determine if you are over the legal limit. BAC is a measurement of how much alcohol is in the bloodstream—0.10% BAC means your blood is currently made of 0.10% alcohol. When you get pulled over, police officers will usually carry handheld breathalyzer devices. 

How Breathalyzers Work

Breathalyzers vary in design, all of which calculate your blood alcohol content.

  • Older models use chemicals like potassium dichromate, which react with alcohol and indicate levels of alcohol in the blood. When the alcohol reacts with the solution, it turns green. The amount of color change correlates to the amount of alcohol in your system. 
  • Newer devices use fuel cell technology. When you blow into the device, platinum electrodes oxidize any alcohol in the air, creating protons, electrons, and acetic acid in the process. The protons move through the bottom compartment and combine with oxygen to form water. The electrons flow through a wire that connects the two platinum electrodes, creating an electric current. The more alcohol that gets oxidized, the stronger the electric current. The device measures the strength of the electric current and calculates it into a BAC. Simple enough, right?

Refusing a Breathalyzer

Almost every lawyer will advise against refusing a handheld breathalyzer. If you are being pulled over, it is likely that the officer already has a reasonable suspicion that you are drunk and will arrest you anyway. Depending on the state, refusal to take a breathalyzer can be a misdemeanor by law, resulting in a fine or even jail time. It can also mean automatic suspension of your license. 

If an individual is brought to the police station for a DUI arrest, they will use another, more sophisticated breathalyzer. Almost every state requires drivers to take this breath test, so refusal results in license suspension or revocation. These high tech machines use “infrared spectroscopy, where an infrared light passes through a sample of the person’s breath, and the machine measures the amount of infrared radiation that passes through the breath, allowing it to very accurately measure a person’s BAC.”

Ignition Interlock Breathalyzers

Depending on the severity of your situation, some DUI convictions require you to continue taking breathalyzer tests to resume driving. Ignition interlock devices like the Low Cost Interlock hook into your car and test your blood alcohol content before your vehicle starts.

Field Sobriety Test vs Breathalyzer

Field sobriety tests and breathalyzers function in different ways, but they work together to let law enforcement know if you are safe to be on the road, as well as help you avoid another drunk driving incident. 



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