A method of detecting foreign bodies in a medium with a radar having a transceiver, and including emitting a radar wave through a wall surface into the medium with the transceiver, detecting a radar signal reflected in the medium, pre-processing the reflected radar signal and subjecting the pre-processed radar signal to evaluation and assessment, determining a characteristic of a foreign body at a stationary position of the transceiver with an algorithm which is based on a pre-processed, digitalized receivable signal, which characteristic permits to recognize differences between a shape of the reflected radar signal and stored comparison values, and conducting a comparison assessment of the shape differences of the reflected signal against predetermined threshold values.