The present invention relates to a device for determining the characteristic impedance spectrum of a token such as a monetary coin, said device comprising: —a point impedance transducer having an inducing element for inducing an ultrasonic movement in the token and a sensing element for detecting the resistance of the token to that induced movement; —a closed system for housing said point impedance transducer; and processing means connected to the point impedance transducer for determining the characteristic impedance spectrum of said token. In particular, the present invention relates to testing whether a token or coin is genuine or a forgery, of sorting coins including from differing monetary systems and/or their denominations, and also providing a “fingerprint” for forged coins.