Since when do Americans have to declare their constitutional rights out loud in order to claim them?

In the case of crime suspects, the right to remain silent, which has been enshrined in law for decades under the 1966 Miranda ruling, now comes with just such a strange proviso.

As a result of a 5-4 ruling by the Supreme Court on Tuesday, those handy Miranda flash cards that police carry need to be updated to read: Speak up, or you can't remain silent legally.

The ruling in a Michigan murder case narrows a defendant's right against self-incrimination by specifying that a suspect has to voice his intention to invoke his Miranda rights.

Murder suspect Van Thompkins was read his rights, but then implicated himself in a 2000 killing after listening in silence to police questions during a nearly three-hour interrogation.

While a lower court tossed Thompkins' murder conviction, the Supreme Court reinstated it because Thompkins decided to answer an incriminating question.

Had the court merely ruled that Thompkins, by speaking, had waived his right to remain silent, the decision wouldn't have set off such shock waves among rights activists.

But Justice Anthony M. Kennedy's majority opinion also concluded that a defendant can be questioned at length as long as he doesn't clearly announce to police his refusal to answer questions.

Will would-be criminals brush up on constitutional law before committing whatever stupid criminal act they have in mind? Unlikely.

So this ruling tilts in favor of police and continues to chip away at individual liberties - as did recent misguided proposals from President Obama that terror suspects be grilled longer before being Mirandized than now permissible under already reasonable time waivers.

In her stinging dissent, Justice Sonia Sotomayor got it right by saying the Miranda ruling "marks a substantial retreat from the protection against compelled self-incrimination."

The fact that DNA exonerations often upend criminal confessions that turn out to have been coerced after lengthy interrogations demonstrates the risks of such police procedures. That's a key reason Miranda rights were established in the first place under our legal system, which adheres to the ideal of innocent until proven guilty.

With these new police powers, it becomes even more critical to videotape all major-crime interrogations to guard against coercion.

It may seem to some that the high court ruling will enable police to nab more bad guys and make the charges stick. But by setting up a "gotcha" set of rules about a key constitutional protection, the high court has eroded individual liberty for all Americans.