A detection device that can be used for detecting objects behind clothing etc including a dielectric lens and a receive element sensitive to millimetre wave radiation. Prior art systems produce an image of a scene usually using scanning optics. This can be large and expensive. The present invention instead take spot readings from different parts of a scene without building up an image. The spot readings are processed, and an indication given to a user if certain characteristics of the readings are observed. Typical characteristics used are the differences in absolute received power level, and the power level at different polarisations. Such characteristics are typically present is an object of interest is in the scene. Also disclosed are various methods of altering the received beam to get readings from different areas from the scene, such as changing the beam width, or beam angle.