Identify the state in the working telephone line(clear, ring, ). Receive the tone signal on the cables or wires(telephone line). continuity of the cables or wires without damaging the insulation. Send a single solid tone or a dual alternating tone to the object cables or wires. Track cable and identify where a line breaks. Perfect for installing, debuging, maintaining telephone line and other wires or cables. Model: FWT21 Audio Signal: 1.5kHZ Receiving Frequency Range: 100Hz-300kHz Receiver Battery: 1 * 9V 6F22 Battery (Not Included) Emitter Battery: 1 * 9V 6F22 Battery (Not Included) Receiver Size: 238 x 43 x 26mm / 9.4 x 1.7 x 1.0in Emitter Size: 145 x 35 x 25mm / 5.7 x 1.4 x 1.0in Colour:black Material:ABS Size:238 x 43 x 26mm Package Contents: 1 x Transmitter(FWT21 Sender) 1 x Receiver 1 x Carrying Bag 1 x Chinese and English manual Only the above package content, other products are not included. Note: Light reflection 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.