What is the test for an implied waiver of the Miranda rights?

" '[A] suspect who desires to waive his Miranda rights and submit to interrogation by law enforcement authorities need not do so with any particular words or phrases. A valid waiver need not be of predetermined form, but instead must reflect that the suspect in fact knowingly and voluntarily waived the rights delineated in the Miranda decision. [Citation.] We have recognized that a valid waiver of Miranda rights may be express or implied. [Citations.] A suspect's expressed willingness to answer questions after acknowledging an understanding of his or her Miranda rights has itself been held sufficient to constitute an implied waiver of such rights. [Citations.] In contrast, an unambiguous request for counsel or refusal to talk bars further questioning. [Citation.]' [Citation.] [] Ultimately, the question becomes whether the Miranda waiver is shown by a preponderance of the evidence to be voluntary, knowing and intelligent under the totality of the circumstances surrounding the interrogation. [Citations.] The waiver must be 'voluntary in the sense that it was the product of a free and deliberate choice rather than intimidation, coercion, or deception' [citation], and knowing in the sense that it was 'made with a full awareness of both the nature of the right being abandoned and the consequences of the decision to abandon it.' " (People v. Sauceda-Contreras (2012) 55 Cal.4th 203, 218-219.)