A fluid treatment cartridge includes a housing having a fluid inlet and a fluid outlet with a treatment media contained within the housing. The fluid treatment cartridge includes a detection member comprising at least one closed electrically conductive loop having at least two spatially separate sections. Each of the sections generates a magnetic response when at least one section is electromagnetically excited. The magnetic response of each section is predetermined by the physical shape of the section and comprises at least one of a predetermined magnetic phase response and a predetermined magnetic amplitude response. The predetermined magnetic response of at least one other section of the closed electrically conductive loop corresponds to at least a one digit code.