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U.S. Supreme Ct: Warrantless Searches and DUI

Updated: Jan 23, 2021

In a big case out of the U.S. Supreme Court, Justice Alito held that law enforcement may almost always get a blood test without a warrant if the subject is unconscious during a DUI investigation. Mitchell v. Wisconsin, No. 18-6210 (U.S. Jun. 27, 2019)

DUI and the 5th and 14th Amendment

Alito first goes through some of the prior case law that they have decided in regards to the Fifth and Fourteenth Amendments:

DUI and the 4th Amendment

Alito then explains the Court's prior precedent on how the Fourth Amendment applies to warrantless DUI breath tests and blood tests (both are searches).


1.) Consent

Because these tests (in these situations) are without a warrant, they must fall under an exception. The state of Wisconsin had argued essentially that the implied consent statute applied, and thus consent was the exception to the warrant requirement. However, the Court does not seem to think that is applicable necessarily:

“Our prior opinions have referred approvingly to the general concept of implied consent laws that impose civil penalties and evidentiary consequences on motorists who refuse to comply.” Birchfield, 579 U. S., at ___ (slip op., at 36). But our decisions have not rested on the idea that these laws do what their popular name might seem to suggest—that is, create actual consent to all the searches they authorize. Instead, we have based our decisions on the precedent regarding the specific constitutional claims in each case, while keeping in mind the wider regulatory scheme developed over the years to combat drunk driving. That scheme is centered on legally specified BAC limits for drivers—limits enforced by the BAC tests promoted by implied-consent laws.

If consent is not applicable, then what is?

2.) Search Incident to Arrest

First, there is search incident to arrest. The Court has approved this exception under certain, narrow, facts. The Court allows for a warrantless breath test of a conscious subject, but does not allow for a warrantless blood test of a conscious subject:

3.) Exigent Circumstances

Second, there are exigent circumstances. And that's what this case focuses on. The Court explains that exigent circumstances is on a spectrum. At the bottom of that spectrum is simply the fact that alcohol dissipates in the blood system and thus is destroyed. However, the Court has held in McNeely that this fact alone is not enough for a warrantless search under the exigent circumstances exception. On the other end of that spectrum are circumstances where there is an emergency and law enforcement needs to focus on the emergency instead of going to get a warrant, such as in Schmerber.

And that is where Alito thinks that this cases sits. The emergency was that the defendant was unconscious, and that “is itself a medical emergency” that created pressing needs.


“When police have probable cause to believe a person has committed a drunk-driving offense and the driver’s unconsciousness or stupor requires him to be taken to the hospital or similar facility before police have a reasonable opportunity to administer a standard evidentiary breath test, they may almost always order a warrantless blood test to measure the driver’s BAC without offending the Fourth Amendment.”


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