This instrument is used to identify and trace wires or cables without damaging the insulation. It can also be used to test for short circuits and locate open circuits. It can also be used to identify specific phone line conditions to phone line installation, debugging, and maintenance. The instrument includes a transmitter and a receiver an adjustable volume control Compatible with all common tracking audio sources Use RJ-11 sockets, , or alligator clips for easy wired connection Check the continuity of cables or wires Trace cables or wires and diagnose breakpoints Identify the status on the work phone line Transmit single or alternate audio over cables or wires and use audio probes to receive signals Adjustable audio on sound probes Including RJ11 socket for telephone and clip for cables Durable design for many years, -free use Battery: 2 * 9V battery (without battery) Color yellow Material: ABS Size: 255 x 120 x 36 mm Package contents: 1 * cable transmitter 1 * cable receiver Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.