These phone sets are professionally made with the highest quality parts, 100% ready to use right out of the bag and designed to check for continuity and loop check. Made for electricians to work on non-energized single conductor cables and multi conductor cables no matter how long they are. Includes ON/OFF switch, super bright LED light that lets you know when continuity is complete, Velcro ties to secure wire leads, phone storage bag, internal battery and support on how to use through email or phone. Master phone has snap-on alligator clips on and right angle input jacks. Secondary phone has large non-detachable alligator clips making them ideal for control panels, I/O panels and MCC's. Communicate two people loud and clear, no noise or interference. If you have any questions, please feel free to contact us.