According to a first aspect, a secure storage unit includes a plurality of movable trays within a housing and is equipped with a tray selector system for selectively accessing a tray on demand, wherein the selector system is configured to release a selected tray for access by limiting the allowable extent of movement of the tray from a stowed to an accessible position with respect to the storage unit by a pre-determined amount whereby access to selected zones of selected trays is controlled. In an embodiment of the secure storage unit, the selector system includes a plurality of discrete electromechanical locking devices operably juxtaposed with respect to the trays, and configured to be individually selectable for releasing and limiting the allowable extent of movement of the selected tray with respect to the storage unit.