A recent Michigan Supreme Court ruling on police searches of passengers during traffic stops can give people more power to challenge such probes and is expected to affect police training in Metro Detroit and across the state, officials and legal experts say.

“The opinion protects Michigan citizens and visitors against unreasonable police searches,” said Michael Faraone, the Lansing-based attorney for the passenger whose case sparked the decision. “It is a change in Michigan law. State and local police will need to be retrained on what is allowed.”

On Monday, the court ruled in favor of a passenger, Larry Mead, who claimed his rights were violated when police in Jackson County searched his backpack in May 2014 without his consent.

A sheriff’s deputy had stopped the car he was riding in with an expired plate driven by a woman Mead had met earlier that night. The driver was giving him a lift, the ruling said.

The deputy looked in Mead’s backpack after the driver consented to a search of her car. The backpack held marijuana and methamphetamine.

Mead eventually was arrested, convicted as a fourth-offense habitual offender and sentenced to serve two to 10 years in prison.

In its unanimous decision, the state Supreme Court said the search was unconstitutional.

“…A passenger’s personal property is not subsumed by the vehicle that carries it for Fourth Amendment purposes,” the ruling stated, referring to the amendment that protects against unreasonable searches and seizures. “…A person can get in a car without leaving his Fourth Amendment rights at the curb.”

The decision overruled the court’s previous 2007 decision that stopped passengers from challenging a search of a car in which they were traveling.

Chief Justice Bridget McCormack noted Mead had “a legitimate expectation of privacy in his backpack that society is willing to recognize as reasonable,” which are key in invoking the Fourth Amendment’s protections, and said police can’t search a passenger based on consent from a driver.

McCormack compared the situation to someone using a ride-sharing service.

“Because (the driver) did not have apparent common authority over the backpack, the search of the backpack was not based on valid consent and is per se unreasonable unless another exception to the warrant requirement applies,” the court ruled.

The ruling is significant “because it cleared up an area in which the Supreme Court had gotten the law wrong,” said David Moran, a University of Michigan law professor who leads the Michigan Innocence Clinic. “…The Fourth Amendment is all about common sense and reasonable expectations of privacy and social norms. It’s just common sense that the police will now need to ask passengers: ‘Mind if I search that bag?’”

In a statement, Michigan State Police spokeswoman Shanon Banner said: “We are reviewing the ruling and will publish a legal update to ensure our members are aware of the case-specific circumstances of this ruling.”

The Michigan Commission on Law Enforcement Standards, which sets training guidelines at the state's basic training academies for officers, has reviewed the curriculum at those sites, contacted the leaders there as well as pored over the state licensing exam to see if any adjustments are needed, executive director Tim Bourgeois said. No changes are expected at this point, he added.

“In general, these changes occur from time to time and law enforcement adjusts to them," Bourgeois said.

Many law enforcement agencies routinely update training for their personnel and anticipate having to tweak instructions based on legal developments, said Robert Stevenson, executive director of the Michigan Association of Chiefs of Police, which has about 1,100 members statewide.

“Within our profession, I’ve not seen shock" over the ruling, he said. "It’s just a further tuning of the search and seizure laws. It’s not a complex concept.”

Others believe that, however training changes, police officers will work to comply.

“Our professional and hard-working men and women law enforcement officers are extremely adept and adaptable to changes in the law,” said Chris Tomasi, assistant general counsel of the Police Officers Association of Michigan, a public employee labor organization. “Officer safety is always at the forefront of our goals and objectives and should also be for the administration.”

Faraone, whose client served two years and then was discharged from parole, described the order as transformative.

“Until this opinion… if anyone took a ride from a stranger, and the driver is stopped for a traffic infraction, and if the driver consents to a search of their car, the police might dig through your purse or backpack even if they had no reason to believe that it contained contraband,” he said.

Associated Press contributed to this report.