Southwire Pro 40136N AC non-contact voltage (NCV) pen tester a valuable addition to your tool bag. Use it whenever you perform electrical work to identify where voltage is present. Detects voltage in wires, light switches, circuit breakers, outlets and light fixtures. Press the On button and the detection tip glows green. Move the detector tip close to the electrical wire or device being tested. If voltage is detected, the detection tip will change from green to red and begin flashing. The NCV will also beep loudly. The 40136N can also be inserted directly into electrical outlets to verify operation. All Southwire non-contact voltage detectors come with a built-in focused LED flashlight so you can illuminate dark areas. Auto power off feature helps conserve battery power. Silent Mode allows you to silence the beeper for quiet areas like hospitals, office buildings, and schools. As an added safety feature, the 40136N has a low-battery self test which periodically checks the condition of the batteries. If battery voltage becomes too low, the self-test circuit turn off the non-contact voltage detector until the batteries are replaced. The 40136N is UL listed. Not designed for use with Tamper Resistant (TR) outlets.