What is the current state of the law requiring an explicit warning from the police for consensual detention?

The right to be free from momentary detention by police is less important than, for instance, the two rights we have just referred to. (People v. Manis (1969) 268 Cal.App.2d 653, 665-666, 74 Cal.Rptr. 423.) Therefore, as we have indicated, the law requires no such explicit warning from police for consensual detention to occur, given the presence of other factors. A warning is not a sine qua non of consensual detention. Neither is knowledge of the right to refuse essential to effective consent. (Schneckloth v. Bustamonte (1973) 412 U.S. 218, 234, 93 S.Ct. 2041, 2051, 36 L.Ed.2d 854.) Such an advisement nonetheless weighs heavily in favor of such consensuality.

Obviously, the more consent is informed, the more likely it is to be voluntary.