In California, a suspect who wishes to waive his Miranda rights and submit to interrogation by law enforcement authorities need not do so with any particular words or phrases." (People v. Cruz (2008) 44 Cal.4th 636, 667.) Miranda v. Arizona (1966) 384 U.S. 436, provides "the prosecution may not use statements, whether exculpatory or inculpatory, stemming from custodial interrogation of the defendant unless it demonstrates the use of procedural safeguards effective to secure the privilege against self-incrimination." (384 U.S. at p. 444.) Once properly advised of Miranda rights, a suspect may waive them provided the waiver is voluntarily, knowingly and intelligently made. (Id. at p. 479.) "'"Under the familiar requirements of Miranda, . . . a suspect may not be subjected to custodial interrogation unless he or she knowingly and intelligently has waived the right to remain silent, to the presence of an attorney, and to appointed counsel in the event the suspect is indigent."' " (People v. Samayoa (1997) 15 Cal.4th 795, 829.) "To establish a valid waiver of Miranda rights, the prosecution must show by a preponderance of the evidence that the waiver was knowing, intelligent, and voluntary." (People v. Nelson (2012) 53 Cal.4th 367, 374-375 (Nelson).) "Determining the validity of a Miranda rights waiver requires 'an evaluation of the defendant's state of mind' and 'inquiry into all the circumstances surrounding the interrogation' ." (Nelson, supra, 53 Cal.4th at p. 375.) "When a juvenile's waiver is at issue, consideration must be given to factors such as 'the juvenile's age, experience, education, background, and intelligence, and . . . whether he has the capacity to understand the warnings given him, the nature of his Fifth Amendment rights, and the consequences of waiving those rights.'" (Ibid.) "This is not to say that a child's age will be a determinative, or even a significant, factor in every case." (J.D.B. v. North Carolina (2011) 131 S.Ct. 2394, 2406.) "Although a juvenile's request to speak with his parent will normally be construed as an invocation of his Fifth Amendment rights , police interviewers are not obliged to advise a juvenile suspect of a right to speak with parents or have them present during questioning ." (In re Aven S. (1991) 1 Cal.App.4th 69, 76.) When a suspect is interrogated on more than one occasion and was advised of, and validly waived, his Miranda rights in an earlier interrogation, "'readvisement is unnecessary where the subsequent interrogation is "reasonably contemporaneous" with the prior knowing and intelligent waiver. The courts examine the totality of the circumstances, including the amount of time that has passed since the waiver, any change in the identity of the interrogator or the location of the interview, any official reminder of the prior advisement, the suspect's sophistication or past experience with law enforcement, and any indicia that he subjectively understands and waives his rights.'" (People v. Pearson (2012) 53 Cal.4th 306, 316-317.) In addition to the prophylactic Miranda advisement requirements, a confession must be voluntary under all the circumstances. "The test for determining whether a confession was voluntary is whether the questioned suspect's will was overborne at the time he confessed. A confession is involuntary under the federal and state guaranties of due process when it has been extracted by any sort of threats or violence, or obtained by any direct or implied promises, however slight, or by the exertion of any improper influence. Coercive police activity is a necessary predicate to a finding that a confession was involuntary under both the federal and state Constitutions." (In re Joseph H. (2015) 237 Cal.App.4th 517, 534.) When a court's decision to admit a confession is challenged on appeal, we accept the trial court's determination of disputed facts if supported by substantial evidence, but we independently decide whether the challenged statements were obtained in violation of Miranda or were involuntary or coerced. (People v. Lessie (2010) 47 Cal.4th 1152, 1169 (Lessie); In re Joseph H., supra, 237 Cal.App.4th at p. 534.) The prosecution has the burden of proving by a preponderance of the evidence that the defendant's waiver was knowing and voluntary. (People v. Smithson (2000) 79 Cal.App.4th 480, 498-499.) "We have recognized that a valid waiver of Miranda rights may be express or implied." (Ibid., citing People v. Whitson (1998) 17 Cal.4th 229, 246, and People v. Cortes (1999) 71 Cal.App.4th 62, 69; see also North Carolina v. Butler (1979) 441 U.S. 369, 373 "waiver can be . . . inferred from the actions and words of the person interrogated".) In California, when a defendant affirmatively states he understands his Miranda rights and then speaks with the police, he generally will be found to have waived his Miranda rights. (See People v. Whitson (1998) 17 Cal.4th 229, 249-250 although officers did not obtain express waiver of Miranda rights, defendant's indication he understood his rights and subsequent response to questions showed knowing and intelligent agreement to speak with authorities; People v. Sully (1991) 53 Cal.3d 1195, 1233 defendant implicitly waived Miranda rights when, after being admonished of those rights, he responded affirmatively that he understood them and gave a tape-recorded statement to the detective.) "Although there is a threshold presumption against finding a waiver of Miranda rights (North Carolina v. Butler, supra, 441 U.S. at p. 373), ultimately the question becomes whether the Miranda waiver was knowing and intelligent under the totality of the circumstances surrounding the interrogation." (People v. Cruz, supra, 44 Cal.4th at p. 668.) "In considering a claim that a statement or confession is inadmissible because it was obtained in violation of a defendant's rights under Miranda . . . , we accept the trial court's resolution of disputed facts and inferences, and its evaluation of credibility, if supported by substantial evidence. Although we independently determine whether, from the undisputed facts and those properly found by the trial court, the challenged statements were illegally obtained citation, we ' "give great weight to the considered conclusions" of a lower court that has previously reviewed the same evidence.'" (People v. Wash (1993) 6 Cal.4th 215, 235-236.)