Implied Consent to DWI Blood Tests and Other Searches

 Posted on July 08, 2026 in DUI/DWI

With drunk driving continuing to be a national issue, advocacy groups have pushed legislatures to institute new laws that would both increase convictions and penalties for drunk driving. One example of these laws is an implied consent law. These provisions allow police to take a sample of the driver's blood or breath, even if the driver objects, in order to determine if a driver's blood alcohol concentration meets or exceeds the relevant legal limit. Texas, with its aggressive policing of driving while intoxicated, is one of the states with an implied consent law. If you are facing a DWI charge in 2026 and have questions about your rights, the Houston DWI defense lawyers at Murphy & McKinney Law Firm, P.C. are here to help.

The basic premise of these laws is that driving is not a right but a privilege granted to you by the state and subject to regulation and limitation. Therefore, if someone obtained a driver's license, they had automatically given the state implied consent to give a blood or breath test anytime they were driving, and the police had probable cause to pull them over.

While these implicit consent laws seem to be narrow in application, given that they are expressly related to drunk driving, the laws implicate several foundational constitutional issues.

Nationally, the validity of a search with implied consent is still in flux, so it's useful to explain the state of the law and police practice in Texas at this point.

And as unclear as the law is at this point, one thing is certain. It is vital to have a DWI Specialist for your defense, someone who knows the current legal issues that render a prosecutor's case more vulnerable, someone who will use every relevant piece of fact and law to fight for you every step of the way.

What Is the Basic Framework for Search and Seizure in DWI Cases?

To understand the current controversy, it's useful to put it into context. First, the Fourth Amendment to the Constitution prohibits the police from conducting a warrantless search of your person or property.

Courts have decided that a breath test and blood test both constitute a search, and the starting point for analysis is that the Fourth Amendment's warrant requirement applies in these cases. Relatedly, the courts have also decided they can yield admissible evidence that can be used against a defendant at trial. Using analysis of someone's blood to convict that person is not considered self-incriminating testimony, which would be barred under the Fifth Amendment.

However, exceptions have been found to the requirement that police must obtain a warrant before getting a blood or breath sample. One such exception is if there are exigent circumstances.

The Exigent Circumstances Exception

From the legal perspective, exigent circumstances exist when there is a compelling need for official action, but there is no time to secure a warrant. In application, that's often been understood to describe a situation where there is a risk that evidence would be destroyed during the time that it would take for the police to obtain a warrant.

Under Texas Transportation Code Section 724.011, any person who operates a motor vehicle in a public place is deemed to have consented to the taking of a specimen of breath or blood if lawfully arrested for a DWI offense. This statute forms the foundation of Texas's implied consent framework and is the starting point for understanding how these searches are legally justified.

What Has the Supreme Court Said About DWI Blood and Breath Tests?

The United States Supreme Court has explored the nature of the breath and blood tests, in light of the tension between the Fourth Amendment's warrant requirement and the implied consent statutes.

Missouri v. McNeely

In 2013, the Supreme Court issued the first of these decisions, Missouri v. McNeely. In McNeely, the State of Missouri had essentially argued that people metabolize alcohol and therefore the evidence, the blood alcohol level, was essentially at risk of destruction, to the point that a blood test could be done without consent under the exigent circumstances exception. As Chief Justice Roberts wrote, alcohol dissipates from the bloodstream at a rate of 0.01 percent to 0.025 percent per hour, meaning evidence is literally disappearing by the minute. Nevertheless, the Supreme Court rejected Missouri's argument and decided that the police needed a warrant before taking a blood sample. Building on earlier court precedent, the court held that the process of alcohol dissipation on its own was not enough to be considered an exigent circumstance. Instead, the court relied on a two-part test: exigency only applied when there was BAC dissipation and some other factor that creates pressing health, safety, or law enforcement needs.

Birchfield v. North Dakota

Then, in 2016, the Supreme Court limited the warrant exception in Birchfield v. North Dakota. In that case, North Dakota had an implicit consent statute that made it a crime to refuse a blood or breath test. The court split the difference on this, holding that the police needed a warrant to do a suspect's blood test, so it should not be a crime to refuse the test, but they could require a suspect to submit to the breath test without a warrant, and refusal could be criminal, because a breath test was not as intrusive and invasive as a blood test.

Mitchell v. Wisconsin

Then in 2019, the Supreme Court looked once again at the limits of implied consent in Mitchell v. Wisconsin. In Mitchell, the police gave a blood test to a DWI suspect while he was unconscious. The Supreme Court upheld this as a valid search, on the grounds that this was an exigent circumstance: The BAC was disseminating, and the suspect was unconscious. His own need for medical treatment met the second element of the urgency needed for a warrantless search. The plurality opinion further said that this would seem to apply any time that the suspect was unconscious.

Going forward, these cases haven't directly ruled on the validity of the implied consent laws themselves, but they have sort of built support for them in terms of the related issues.

What Does Texas's Implied Consent Law Mean for DWI Defendants?

As with many states, Texas has an implied consent law. The law requires people to submit to a breath or blood test. If you refuse, your driver's license can be suspended under Texas's Administrative License Revocation program. However, in State v. Villarreal, the Texas Court of Criminal Appeals held that the implied consent statute does not by itself create an exception to the Fourth Amendment's warrant requirement. Police generally still need either voluntary consent or a valid warrant before obtaining a blood sample unless another recognized exception applies.

More recently, in the 2019 case of State v. Ruiz, the Texas Criminal Court of Appeals found that an unconscious person is not capable of consenting to a blood test. Instead of interpreting Mitchell to mean that any unconscious person may be given a blood test, the appellate court seems to be requiring that courts must do the analysis to see if exigent circumstances exist. That same year, the appellate judges also ruled in a different case that the police could not repurpose an unconscious person's blood sample taken for medical treatment for a BAC test.

Going forward, for breath tests, it seems that it will be increasingly difficult to challenge a breath test because it was warrantless. Instead, the defense's focus will likely be more centered on other procedural aspects of the arrest, such as whether there was reasonable suspicion to stop the driver, whether there was sufficient probable cause to conduct the search in the first place, and whether the results were accurate.

There is less clarity in terms of the validity of a warrantless blood test. But at this point, in Texas, DWI defense attorneys seem to still have grounds to challenge a warrantless blood test. The police will need to establish that there was a real emergency that demanded their attention and resources, to the point that they could not provide those services and pursue a warrant at the same time.

The bottom line is that you can still refuse a breath test, but if you do so, the police will probably go get a warrant to get a blood test. If they don't, the blood test could be thrown out.

What Are No Refusal Weekends in Texas?

While the state's implied consent law was partially overturned, the state still has what it calls No Refusal Weekends. While the name suggests that the state is relying on implied consent to get blood or breath tests, that's not actually what's going on here. The no refusal weekends do not depend on implied consent at all. Instead, if a driver actively refuses to submit to a test, they are simply obtaining the warrants through a temporarily expedited process.

Why Should You Fight a DWI Charge in Texas?

If you've been arrested and forced to submit to a test you did not consent to, you may have legal recourse.

If you wonder whether it is even worth fighting a DWI, the answer is yes, it is. First, remember that a criminal charge is not a conviction. People can and do win a DWI defense. But to do that, get a DWI Specialist.

It's also worth fighting because a DWI can impact every aspect of your life.

Contact Our Houston DWI Defense Attorneys

With 20 years of experience in the courtroom, Attorney Doug Murphy is, year after year, recognized as one of the Best Lawyers in America by US News and World Report and as a Texas Super Lawyer, and Murphy was named Houston's Lawyer of the Year by Best Lawyers in America. One of only two attorneys in the state of Texas who is Board Certified in both Criminal Law and DWI Defense, Murphy is the Dean of the National College for DUI Defense conducted at Harvard Law School. Previously, Murphy also served on the board of directors and as co-chair of the DWI Committee with the Texas Criminal Defense Lawyers Association.

If you're in Texas facing DWI charges, contact the Houston DWI defense lawyers at Murphy & McKinney Law Firm, P.C. today to discuss your case and begin working on your defense. Call 713-229-8333 to get started right away.