Rugged, hand-held and easy-to-use fiber optic test instrument designed to detect and measure the core power levels of optical signals on single-mode optical fiber without disrupting traffic on that fiber. The OFI-400 is simply clamped onto a fiber and indicates the presence and direction of traffic, CW signals and 270, 330, 1000 and 2000 Hz test tones. It allows technical personnel to unambiguously identify a specific fiber and eliminates the risk of accidental disruption of revenue service. The OFI-400 uses a unique optical head design featuring a two-position plunger that enables it to be used with 250 µm, 900 µm and ribbon fiber or 2 mm and 3 mm jacketed fiber. Low insertion loss for in-service ID tasks. Designed for real-world use with rugged, drop-proof construction, ergonomic trigger and integrated backlit LCD. Includes user guide, 2 AAA batteries and a soft carry case (ordering variants vary).