The Fisher Labs FX3 Ferro-Magnetic Probe is easy to operate: simply turn it on and go. This model features motion detection - the tube probe must be moving to detect a target. When the two sensors come across a large ferrous object, the signal tone increases in pitch and volume. When the probe is directly over the target, the signal becomes silent and picks up again when moved past the target. The FX3 is extremely sensitive to iron objects with a large surface area, highly magnetized objects and long objects buried vertically. Large or small, if it's ferrous, the FX3 is designed to find it.

The FX3 uses differential induction to locate iron and steel relics, property markers, pipes and other large ferrous objects buried beyond the reach of ordinary metal detectors. Two sensors respond only to the magnetic field of ferromagnetic objects, ignoring all other materials (copper, aluminum, brass, etc.). As a target is approached, the VCO (Voltage Controlled Oscillator) circuitry responds with an increase in pitch and volume then nulls directly over the target.