The Transponder Peg is a sealed unit that contains a passive tuned L – C resonant circuit, which resonates at a frequency of 101.4 kHz. The peg is buried vertically in the ground along the route of and above a non-metallic optical fibre cable. It enables the cables path to be relocated and traced in the future, when using a portable detecting instrument. The transponder peg can be used for other telecommunication plant located underground e.g. repair joints. The peg contains a ferrite core rod, that must not be broken during handling or installation, otherwise the peg will not work. The peg is completely waterproof and vermin resistant, to achieve a long service lifetime.