Stop guessing if it's working. Know with FiberLert. https://bit.ly/Get_FiberLert Quickly check fiber activity, polarity, and connectivity with FiberLert. Just place in front of the fiber end face or port and a light and tone indicate an active fiber (850 nm to 1625 nm) - no setup or interpretation required. This pocket-sized tool tests single-mode, multimode, UPC and APC patch cords and ports with a non-contact / non-contaminating detector. The LightBeat™ feature flashes the LED, indicating a powered-on condition and good battery and a timer shuts FiberLert™ off after five minutes of inactivity to extend battery life (2xAAA, included). Rugged design includes a convenient pocket clip and is backed by a two-year warranty.