Abstract: Apparatus for receiving and acknowledging the return of a wheeled vehicle to a check-in station, as for example, a grocery service cart. The apparatus includes a rugged, foolproof sensor required to operate in predetermined sequence thereby to thwart efforts to decipher the mode of operation needed to give a false acknowledgment of a returned vehicle or permitting reception of the same vehicle more than once from the same person. All sensor components are adapted to be mounted on a base plate supporting a return entry port and passageway. The apparatus is readily adjustable to accommodate vehicles of different size. Access to control components is safeguarded by a locked cover equipped with tamperproof retainers and means for preventing reassembly of the sensor cover by persons who have gained access without authorization.