In South Dakota v. Opperman, 428 U.S. 364 (1976), the majority observed that police frequently impound vehicles as part of their "community caretaking" function, and an inventory search of a vehicle, once lawfully impounded pursuant to this function, furthers three legitimate purposes: the protection of the vehicle owner's property while in police custody, the protection of police against claims of loss or damage to items within the vehicle, and the protection of police from potentially dangerous items that might be within the vehicle. (Id. at pp. 368-369.) The Opperman court emphasized that the critical issue under the Fourth Amendment is whether a search is unreasonable, and reasonableness must be determined under all the circumstances. (Opperman, supra, at pp. 372-373.) The majority concluded that an inventory search of a locked vehicle, conducted pursuant to "standard police procedures" after the vehicle was lawfully impounded, was not "unreasonable." (Id. at pp. 372, 376.) The Opperman court emphasized, however, that the critical issue under the Fourth Amendment is whether a search is unreasonable, and reasonableness must be determined under all the circumstances. (Id. at pp. 372-373.) Thus, only if officers are warranted in impounding a vehicle, a warrantless inventory search of the vehicle pursuant to a standardized procedure is constitutionally reasonable. (South Dakota v. Opperman, supra, 428 U.S. at p. 372.) The Supreme Court identified three distinct reasons for allowing inventory searches when a vehicle is impounded: (1) the protection of the owner's property while the vehicle remains in police custody; (2) the protection of the police against claims or disputes over lost or stolen property; (3) the protection of police from potential danger. (Opperman, supra, 428 U.S. at p. 369; see also Wells, supra, 495 U.S. at p. 4.) Indeed, "when vehicles are impounded, local police departments generally follow a routine practice of securing and inventorying the automobiles' contents." (Opperman, supra, at p. 369.)