It's like a nitrous trigger for your amp.

Sleek yet heavy-duty 3-button footswitch allows you to choose among ultra channel, crunch channel, clean channel, and effects loop. LEDs indicate operation. Uses a 7-pin DIN plug. Works with XXX and XXX 212 Combo.

Peavey Triple XXX Footswitch Features:

3 buttons
4-function operation
LEDs for clear indication
7-pin DIN plug
Works only with XXX head and XXX 212 combo