Walker by Clarity WTS-501 Line Test Set Integrated Circuit Voice Network Provides Optimum Receive & Transmit Levels & Controlled Side tone Without Drawing Excessive Current Lightweight & Durable Talk/ring Monitor Switch High-impedance Monitor Will Not Disturb Data, Conversations Or Signing 10 Number Memory Storage With 3v Lithium Battery (cr 2023) Walker by Clarity line test set DTMF tone/pulse switchable dial pad to test signals 3-position volume control for up to 12dB of gain Polarity indicator Includes cloth covered cord equipped with anchored strain relief, modular RJ11X plug, two 5-way test clips, and spade connector cord