English: A crystal detector, an antique electrical component used in early crystal radio receivers in wireless stations around the first decade of the 20th century which functioned as a crude semiconductor diode to demodulate the radio signal. Unlike the more common cat whisker detector which used a contact between a crystal and a wire, this type used a contact between two different crystals. In this particular example the crystals are silicon and arsenic. Several pieces of silicon are mounted on the round holder (on left). The arsenic crystal (on right) position is adjusted by means of the horizontal shaft equipped with knob, until it touches one of the silicon crystals. The set screw equipped with knob, located at top front of the stationary post on right, is then tightened.

This holder, manufactured by G. W. Pickard's Wireless Specialty Apparatus Co., was normally used for Pickard's patented "Perikon" detector, which consisted of a bornite (Cu₅FeS₄) crystal mounted in the adjustable holder (right), and multiple zincite (zinc oxide, ZnO) crystals mounted on the round carousel. The reason for providing multiple samples of zincite was that the zincite crystal was fragile and tended to become damaged and unusable with time. The "Perikon" detector, which stood for "PERfect pIcKard cONtact", was widely used in military wireless stations.