A wall detector (1) for detecting an object (3) embedded in a substrate (2) includes a detection antenna (5) for introducing broadband, high-frequency alternating electric fields (9) of a measurement frequency (f.sub.M) in the substrate (2); a measurement system (6) connected to the detection antenna (5) for measuring the delayed interaction of the alternating fields (9) with the object (3), a calculation device (7) for detecting the object (3) based on the measurement signal and for determining the associated depth information, and a permittivity measurement device (8) with at least one auxiliary potential plate (11) for measuring the permittivity measurement signal of the substrate at a permittivity measurement frequency (f.sub.p) that is a lower than the measurement frequency; and an associated measurement method.