This paper presents a novel technique for the detection and remote reading of passive temperature sensors. This technique is based on a 3D beam scanning performed by a FMCW radar for measuring the echo level of sensors distributed in a scene. The carrier frequency is 24GHz and two frequency modulation bandwidths are investigated (2 GHz and ISM 250 MHz). The fluctuation of the measured echo level is analyzed by using appropriate estimators and the derived temperature variation is displayed by using a convenient three dimensional representation of isosurfaces.