The United States Supreme Court has, over the last two years, re-examined the iconic Miranda warnings. There have been three notable cases decided recently that impose limitations on Miranda and lead many to question the warnings sustainability.
Powell v. Florida and Maryland v. Shatzer were decided within one day of each other. Powell held that the statement "You have the right to a lawyer before answering any questions and you may invoke that right at any time" was an adequate warning under Miranda even though the officers did not explain that the suspect had a right to a lawyer during interrogation.
Maryland v. Shatzer answered the question of whether a detained suspect who has asked to speak with an attorney can ever be questioned again without a lawyer present. The Court held that law enforcement could resume interrogation if 14 days have passed since the suspect last expressed a desire to have a lawyer present and the suspect has waived his right to an attorney for the current interrogation.
The third case, Berghuis v. Thompson, held that a suspect must unambiguously state he wishes to remain silent. Silence in the midst of questioning is not an adequate invocation of the right to remain silent. In the dissenting opinion, Justice Sotomayor argued that the Court's ruling imposes a counter intuitive requirement on suspects: a person must speak in order to invoke their right to remain silent. Try to reason your way to that conclusion.
While the Miranda warnings are still intact, many feel that the Court is gradually chipping away that the warnings piece by piece. The question is whether the Court will one day see fit to overrule Miranda or just continue to impose limitations upon it. At any rate, as of today a person can no longer remain mute and enjoy the protections that Miranda once afforfded.