The Supreme Court of Wisconsin addressed two important questions surrounding the legality of warrantless blood draws for defendants suspected of driving under the influence.
First, the Court decided that a warrantless blood draw made prior to the decision of the United State’s Supreme Court in Missouri v. McNeely is constitutional because the officer was relying on a good faith understanding of the law at the time. State v. Cassius A. Foster, 2014 WI 131 at ¶58, 12/26/14. This is commonly known as the “good faith” exception to an otherwise illegal search and seizure. As a result, defendants who have been subjected to a warrantless blood draw prior to the Missouri v. McNeely decision are out of luck.
The Court also clarified whether the dissipation of blood alcohol concentration over time may satisfy the “exigent circumstances” exception so that an officer can perform a warrantless blood draw. The Court held that “exigent circumstances justify a warrantless blood draw if delaying the blood draw would ‘significantly undermin[e] [its] efficacy.'” State v. Michael R. Tullberg, 2014 WI 134 at ¶50, 12/26/14. As a result, it appears that the Court is leaning toward justifying any warrantless blood draw because the dissipation of alcohol over time ‘would significantly undermine the tests efficacy’ if it is not done promptly.
Padway Criminal Law Blog 
[…] January 2, 2015January 5, 2015 Aaron DeKosky Traffic and OWIDrunk Driving, DUI, OWI, Warrant The U.S. Supreme Court in Missouri v. McNeely held that a police officer cannot automatically order a blood test on a driver that was lawfully arrested for OWI (operating while intoxicated). Instead, the officer must first obtain a warrant absent exigent circumstances. Importantly, the simple fact that blood alcohol concentration diminishes with the passage of time is insufficient to establish exigent circumstances. The Wisconsin Supreme Court issued decisions clarifying this decision. Read about the updates here. […]
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