Fisher Gemini-3

The Fisher Gemini-3 is a two-box detector made for finding large, deep metal objects rather than small coins. A separate transmitter and receiver are held apart on a handle, which lets the system look much deeper than a normal coil but ignores items smaller than roughly a baseball. It traces its history to Fisher's 1930s ground-penetrating detector patent. It is a specialised tool rather than an everyday hobby detector for coins and jewellery.

It runs on an 82 kHz crystal-controlled frequency and offers four modes: Inductive Trace, Conductive Trace, and Wide-Scan and Narrow-Scan Inductive Trace. Wide-scan can be used by one or two operators for sweeping larger areas. A variable-pitch VCO audio response guides you to the target, and battery test meters and 60-cycle noise reduction are built in. These modes let the operator switch between searching open ground and tracing a known line.

Fisher's dealer description states it can detect large objects as deep as twenty feet or more, depending on target size and ground mineralisation; real results will vary. It weighs about 7 lb, uses 16 AA batteries for around 50 hours and is not waterproof. In Pakistan it suits cache searches, tracing buried pipes and locating large metal objects. Users should treat depth figures as a best case, since smaller objects will not be detected that deep.