How has the court interpreted consent to accompany a police interview?

For his initial interview, defendant accompanied two detectives from his home to the sheriff's department. There, he was interviewed for two hours, and then driven to his mother's home. Defendant claims that his consent to accompany the detectives was not voluntary and was instead the product of an implied assertion of authority. The trial court ruled that defendant's consent was clearly voluntary. We review the trial court's characterization of defendant's contact with the detectives as a consensual encounter independently, but we review its factual findings under the deferential substantial evidence standard. (People v. Zamudio (2008) 43 Cal.4th 327, 342, 75 Cal.Rptr.3d 289, 181 P.3d 105.)