Dedicated DUI Defense Attorney Backed by Over Two Decades of Experience

Blood/Breath Tests

It is illegal in California to operate a motor vehicle when your blood alcohol concentration is at or above .08%. Blood alcohol concentration (BAC) refers to the amount of ethyl alcohol in your blood stream. According to the DUI laws in California, when your BAC level reaches or exceeds .08%, you are no longer able to safely and competently operate a vehicle. This is because the consumption of too much alcohol hinders your attentiveness, reaction time, and physical and mental coordination.

If a police officer suspects you of driving under the influence, he or she will test your BAC to determine if it is higher than the legal limit. Blood alcohol concentration can be tested in one of two ways: by means of a blood test or breath test.

Blood Test

Blood testing is the most accurate way to test a driver’s blood alcohol concentration. To conduct a blood test, blood is drawn from the driver’s arm and analyzed in a laboratory. The results of the test indicate whether or not the driver’s BAC is above .08%. If it is, then he/she will be charged with DUI.

Breath Test

Breath testing is the most popular modality for testing blood alcohol concentration. To conduct a breath test, the driver blows into a breathalyzer machine. The machine then measures the driver’s breath alcohol concentration, which is said to correlate with his/her blood alcohol concentration. After the driver blows into the machine, the machine will indicate his/her BAC. If his/her BAC is .08% or higher, then he/she will be arrested and charged with DUI.

Challenging a Breath Test

If you were arrested for DUI after submitting to a breath test, it’s important to hire an attorney to represent you in court.

Breathalyzer machines are not 100% accurate, and there are numerous factors that can cause them to give an inaccurate reading, such as:

  • Radio frequency interference
  • Whether the officer knows how to properly use the machine
  • Mechanical defect
  • Your gender and weight
  • The amount and type of alcohol you consumed
  • If you ate any food prior to taking the test

A skilled DUI attorney can challenge the accuracy of your BAC test results, and ensure that the arresting officer executed the test properly and did not arrest you without just cause.

Am I Required to Take a Breath or Blood Test?

Contrary to popular belief, YOU ARE NOT REQUIRED by California state law to take a breath or blood test. However, if you refuse to submit to testing at the request of an officer, your driver’s license will automatically be suspended. In addition, your refusal will be used as evidence against you in court, and it may result in an increase in penalties if you are convicted of the charges.

Contact Contra Costa DUI Lawyer Robert Tayac

If you or someone in your family has been arrested for DUI after submitting to a breath or blood test, Contra Costa DUI attorney Robert Tayac can handle your case, and defend you in court. Mr. Tayac has handled countless cases in which he has successfully challenged the results of a breath or blood test to win his clients’ cases. With over 20 years of experience in DUI law, Mr. Tayac has gained the knowledge and skill to develop effective legal strategies and build a strong defense. Furthermore, Mr. Tayac is committed to protecting your best interest at all cost, and ensuring you are not convicted on DUI charges.

To speak with our firm's Contra Costa DUI lawyer Robert Tayac, please call 925-288-9800 today!

Why Choose Our Firm?

Attorney Robert Tayac Puts a Long, Decorated Career to Work for You
  • Puts Over 20 Years of Experience Toward Your Case

  • Specialized Education in DUI Defense

  • Has Trained Other Attorneys in San Francisco

  • Former San Francisco Police Officer & Police Inspector

  • Certified by the SFPD on the Intoxilyzer 5000 Testing Device

  • Co-Authored the 4th Edition of California Drunk Driving Defense

  • Boasts a Successful Record Achieving the Best Result for His Clients

  • Takes the Time to Understand You & Your Case

Client Testimonials

  • “These clients have called me to thank me for referring them to the Law offices of Robert Tayac.”

    R.R., Attorney at Law

  • “Without Mr Tayac's knowledge and drive to succeed, I most likely would not be able to write this review today.”


  • “His in depth knowledge and expertise within his field, along with deep and lasting relationships with the District Attorneys office and everyone involved are without a doubt unmatched.”


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