The present invention exploits extreme sensitivity to initial conditions in ray-chaotic enclosures to create a method to distinguish nominally identical objects through their unique “wave fingerprints.” The fingerprint can be measured through transmission of a pulsed microwave signal as a function of carrier frequency and time. When internal components are re-arranged, the Electromagnetic Fingerprints (EMF) changes in significant ways. The EMF can be detected by direct injection measurements of the enclosure or through remote measurement.