A reader for a secure tag. The reader comprises a first excitation source (such as one or more LEDs) that stimulates at least one transition in the secure tag. The reader also comprises a second excitation source that stimulates more transitions than were stimulated by the first excitation source. The reader has a detector for detecting luminescence from the secure tag in response to excitation from the first excitation source and in response to excitation from the second excitation source to ensure that luminescence is detected at a pre-determined wavelength in response to the second excitation source but not the first excitation source.