The NL-4 Sniffer/Sender from SoundTools is a remote end cable tester with a Sniffer unit that reads the status of the cable and a Sender unit as the power source. It can be used to test speaker lines and cables when the ends are at a distance in live and rehearsal applications. Utilizing phantom power, the Sniffer end tests speaker lines in minutes and displays a readout of 3 simple LEDs with the diagnosis of your cable. The NL-4 Sniffer/Sender tests for every possible short-circuit, open, or cross wire in NL-4 cables. If the LEDs read all green, your cable will work.