They are not very helpful for cable runs more than a few meters, or when the cable not visible or accessible, or when the laser light can''t penetrate the jacket. VFLs work well for exposed lengths of fiber near a patch panel by illuminating bad connections and breaks. Fluke Networks Mulitmode Fiber Distance and Fault Locator - Network Traffic Monitoring, LAN Cable Testing, Cable Fault Testing, Mismatched Wiring Testing, Fiber Optic Cable Testing, Network Testing - Optical Fiber - 2Number of Batteries Supported - AA - Battery Included - Alkaline