This effect is a natural continuation of the probe series... the fuzz factory probe, the volume control/manual tremolo probe, and now a wah. It's probably exactly what you think it is: a theremin-style antenna controlling a wah, getting brighter as your foot approaches. It has one extra feature, however. There's a Super Hard-On boost circuit in front of the wah, with a knob to set the exact level of boost for driving your wah sound. It can be turned up high enough to make the wah crack up a little for that "something's gonna blow" sound. It gets pretty darn loud!
How it works: The probe circuit generates a small (one or two inches high) "bubble" of RF energy at about a million cycles per second above the copper plate. As your foot or hand (or any wet or metallic object, for that matter) approaches the copper plate, the RF field is disturbed and the circuit reacts by increasing the brightness of an LED, which drives a photoresistive cell and controls the Z. Vex wah circuit. The wah circuit is actually the Seek-Wah sound circuit without the sequencer control. It's also the same wah circuit as the one in The Drip guitar that I make. The only difference is the boost circuit in this Wah Probe model.