Apparatus (200, 300) for detecting a concealed object in an article (205, 305) comprising: a source (210, 310) of Near Infra-Red radiation comprising a plurality of light emitting elements at different respective spatial locations, the source operable to illuminate the article to be inspected; a detector (220, 320) comprising a plurality of photodetector elements, the detector being operable to output respective values of intensity of NIR radiation incident upon the photodetector elements, respective photodetector elements having an optic axis substantially coincident with an optic axis of a corresponding source element, the detector being configured to detect that portion of the source beam incident on the detector that has been passed through at least a portion of the article; a collimator (225, 340), the collimator having an entrance aperture, the collimator being arranged to collimate light passing through the entrance aperture that has passed through the article before it reaches the detector; and control means, the control means being arranged to detect by means of the detector an intensity of NIR illumination incident on the detector and to identify without forming an image of the object the presence of a concealed object in the article responsive to a variation in detected intensity across at least a portion of the article; wherein the apparatus is operable to illuminate each source element in turn and to detect by means of the detector light incident thereon from each respective source element in turn at a position of the detector corresponding substantially to a substantially direct path of NIR radiation from each detector through the article. a source (210, 310) of Near Infra-Red radiation comprising a plurality of light emitting elements at different respective spatial locations, the source operable to illuminate the article to be inspected; a detector (220, 320) comprising a plurality of photodetector elements, the detector being operable to output respective values of intensity of NIR radiation incident upon the photodetector elements, respective photodetector elements having an optic axis substantially coincident with an optic axis of a corresponding source element, the detector being configured to detect that portion of the source beam incident on the detector that has been passed through at least a portion of the article; a collimator (225, 340), the collimator having an entrance aperture, the collimator being arranged to collimate light passing through the entrance aperture that has passed through the article before it reaches the detector; and control means, the control means being arranged to detect by means of the detector an intensity of NIR illumination incident on the detector and to identify without forming an image of the object the presence of a concealed object in the article responsive to a variation in detected intensity across at least a portion of the article; wherein the apparatus is operable to illuminate each source element in turn and to detect by means of the detector light incident thereon from each respective source element in turn at a position of the detector corresponding substantially to a substantially direct path of NIR radiation from each detector through the article.