Abstract: An inventory monitoring system and method for monitoring items stored in a pallet rack are described. The inventory monitoring system comprises a pallet rack comprising a plurality of construction elements for storing a plurality of pallets and a rail system mounted to the pallet rack and forming at least one track for guiding at least one vehicle for scanning the pallets, the rail system being located at least partly inside a space defined by outer construction elements. The at least one vehicle thereby is movably mountable to the rail system and adapted for moving over the rail system, the vehicle comprising detection means for detecting information of the pallets which are located in the vicinity of the rail system.