What is a common use for point-contact diodes?

A point-contact diode is constructed by pressing a thin metal wire, often called a 'cat's whisker', against a semiconductor crystal. Because the actual contact area between the metal and the semiconductor is extremely small, the diode has incredibly low internal junction capacitance. This very low capacitance allows the point-contact diode to respond to very high frequencies without shunting the signal, making it exceptionally well-suited for use as an RF detector. It is classically used to demodulate amplitude-modulated (AM) signals in simple receivers. Because the contact point is so small, these diodes are highly fragile and can only handle tiny amounts of current. Therefore, they would instantly burn out if used as a high-voltage rectifier, and they lack the physical characteristics needed to act as constant current or voltage sources.