Set of 2 replacement wires. Eventually, the wires will wear out and need to be replaced. Your kit comes with an extra set of wires, so you will have a spare on hand. A typical symptom of a failing wire is that one pulser will not work. You can order replacement wires from us, or you can sometimes find them in an electronics store. They are standard audio cables. However, be sure to take your pulsers with you to be sure the plugs will fit. If you order from us, a package of 2 will cost $16.00.