Insten Cable Tester for RJ45 / RJ11 Keep your network running smoothly by testing your cables to uncover problematic shorts, open wires, crossing pairs and other wiring mishaps. Use for testing your homemade Ethernet patch cables to make sure they are in working order prior to connecting to your devices. Tests RJ45 cables, RJ11 telephone cables and network cables. Easy to read LED display indicates problems. Hand-held for portability. Detachable master/ remote unit for versatility. Connect cable to both master unit and remote to test cable for problems. Requires one 9V battery (not included).