Which of the following statements about a detainee being interrogated by an informant is true?

The assertion that warnings are not necessary if the detainee does not know the informant is working for the police is based on the principle that the requirement for Miranda warnings hinges on whether an individual is in custody and whether they are being subjected to interrogation that could elicit incriminating responses. If a detainee does not perceive the informant as an agent of the state—particularly if they are unaware that the informant is collaborating with law enforcement—then they may not be deemed to be "in custody" for the purposes of Miranda.

In scenarios involving an informant, if the statements made to the informant are not made under interrogation conditions or while in custody of law enforcement, the presence of Miranda warnings is not mandated. Therefore, the understanding of whether the detainee is aware of the informant's role can be crucial in determining the applicability of Miranda protections.

In contexts where an individual is unaware that they are speaking to a police informant, the courts have recognized that statements made do not engage the protections that Miranda provides. This contributes to the validity of option B as a correct statement concerning the circumstances surrounding interrogations involving informants.