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Most, if not all, states have adopted “implied consent” laws where drivers may be tested if police have probable cause to suspect they have been driving while intoxicated. Drivers may withdraw consent and refuse to take a test, subject to penalties. In Birchfield v. North Dakota (2016) the Supreme Court held that generally police must obtain a warrant to require a blood test (versus a breath test) where officers have probable cause.

But what if a driver is unconscious and unable to withdraw consent to a blood test (and unable to take a breath test)? Wisconsin and 28 other states allow warrantless blood draws of unconscious drivers where police have probable cause to suspect drunk driving.

The question the Supreme Court will decide in Mitchell v. Wisconsin is whether a statute authorizing a blood draw from an unconscious motorist provides an exception to the Fourth Amendment warrant requirement.

In a long-awaited decision in Carpenter v. United States, the Supreme Court held 5-4 that the Fourth Amendment requires the government to receive a warrant to obtain cell-site location information (CSLI).

In the Court’s majority opinion Chief Justice Roberts provides an explanation of how CSLI works. “Cell phones continuously scan their environment looking for the best signal, which generally comes from the closest cell site. Most modern devices, such as smartphones, tap into the wireless network several times a minute whenever their signal is on, even if the owner is not using one of the phone’s features. Each time the phone connects to a cell site, it generates a time-stamped record known as cell-site location information (CSLI).”

In United States v. Carpenter the Supreme Court will decide whether police must obtain warrants per the Fourth Amendment to require wireless carriers to provide cell-site data. State and local governments have an interest in obtaining cell-site data as quickly and easily as possible as it can provide solid evidence a particular person was near the scene of a crime.  

Cellphones work by establishing a radio connection with the nearest cell tower. Towers project signals in different directions or “sectors.” In urban areas, cell sites typically cover from between a half-mile to two miles. Wireless companies maintain cell-site information for phone calls.

In City of Los Angeles v. Patel the Supreme Court held 5-4 that a Los Angeles ordinance requiring hotel and motel operators to make their guest registries available to police without at least a subpoena violates the Fourth Amendment. In his dissenting opinion, Justice Scalia cites to the State and Local Legal Center’s (SLLC) amicus brief, which notes that local governments in at least 41 states have adopted similar ordinances. Eight states also have hotel registry statutes:  Indiana, Florida, Massachusetts, Maine, New Hampshire, New Jersey, Wisconsin, and the District of Columbia.