The Monoprice MCT-470 Pro LAN Tracer/Toner is a professional tool used to test and troubleshoot RJ11 cables and individual wires. It can be used to trace and identify individual wires or cables within a bundle or group and can perform continuity testing. The tester is composed of two individual units: the Tone Generator and the Amplifier Probe with sensing tip. Each unit is constructed of plastic and is powered by a 9 volt battery. Two 9 volt alkaline batteries are included in the packaging. The Tone Generator has a three position toggle switch, that turns the unit on in Tone or Continuity mode. A metal sheath around the switch prevents it from being accidentally turned on or off. A 3-color LED is used to indicate line polarity, continuity, and phone line condition. The Tone Generator unit has an attached pair of red and black leads with alligator clips, plus an RJ11 4-conductor wire and plug. The Amplifier Probe has an adjustable volume control, a speaker, and a 3.5 mm headphone jack. A recessed power/activation press-to-use button prevents the probe from being accidentally powered on or from draining the battery by being left on when not in use. The Amplifier Probe is used to detect the presence of the tone sent by the Tone Generator on a wire. This can be used to detect continuity in a single wire and can test for breakage points along a wire"s length. Additionally, it can be used to identify individual wires within a bundle. *** 30-day easy returns. No restocking fee. Free lifetime technical support. 1 year warranty. ***