The product shown is a 5-in-1 cable tester, model TL-521. This type of device is used to test and troubleshoot a variety of network and computer cables.
It can test five different types of cables: Ethernet (RJ45), 10Base, RJ11, FireWire (1394), and USB.
It checks for continuity, crossover, and short circuits.
The device is designed for use with both shielded (STP) and unshielded (UTP) cables.
It is a portable, palm-sized unit with one-button testing and LED indicators for clear results.