PHOENIX — Police cannot frisk someone they stop and question unless they have some “reasonable suspicion criminal activity is afoot,” the Arizona Supreme Court ruled Thursday.

In their unanimous decision affirming the right to carry a gun without interference, the justices rejected arguments by prosecutors that a simple belief someone is armed and dangerous is enough to justify a search, even without any evidence of criminal activity.

The U.S. Constitution dictates otherwise, justices said.

“The Fourth Amendment protects the right of people to be free from unreasonable searches and seizures,” wrote Justice Rebecca Berch.

“When officers consensually engage citizens on the street without having any evidence of wrongdoing, the mere presence of a weapon does not afford officers constitutional permission to search weapons-carrying individuals,” she said. Any other conclusion would potentially subject countless law-abiding persons to pat-downs just for legally caring a firearm, she said.

Berch said police still can ask people if they are carrying a weapon, and they can ask that person to hand it over while they are talking.

But she also said those individuals remain free to walk away.

The case involves Johnathon Serna, who was questioned by police after they observed him while patrolling what was described as a “gang neighborhood.” The officers described him as “very cooperative and polite.”

But while speaking with him, one observed a bulge in Serna’s waistband and asked him he if had a gun.

When Serna replied in the affirmative, the officer ordered Serna to put his hands on his head and took the weapon.

Serna was arrested after follow-up questions showed he had a felony conviction, meaning he could not legally carry a firearm.

Berch said not all encounters between police and individuals constitute illegal seizures.

“So long as a reasonable person would feel free to disregard the police and go about his business, the encounter is consensual and no reasonable suspicion is required,” she wrote. But it’s what happens when that encounter is no longer consensual.

In this case, she noted, the officer told Serna to put his hands on his head. And the officer said that was an order and not a request.

“A reasonable person would not have felt free to disregard such a command from a law enforcement officer,” Berch said.

“The order and frisk here at issue restrained Serna’s freedom to walk away and thus constituted a seizure for Fourth Amendment purposes,” she continued. “Such a seizure requires constitutional justification.”

Berch acknowledged that concerns requiring an officer to suspect criminal activity before frisking someone might hinder the ability to investigate suspicious behavior.

“But such reasons cannot justify unwarranted infringements on Fourth Amendment rights,” she said. And she said there are “appropriate ways” for officers to protect themselves once they become aware someone is armed, like asking the person to temporarily relinquish the weapon.

“But absent consent, to seize a weapon the officer must justify a frisk with facts sufficient to establish reasonable suspicion of criminal activity — a low standard, readily established in many search settings,” she said.