Fisher Research Labs M-101 Research Metal Detector, Analogue, 4.5 kHz, 12:1

Designed specifically for finding reinforcing bars and other metal objects embedded in concrete, conduits, PK nails, wiring, wall studs, and other metallic objects
A preset circuit eliminates ground effects caused by highly mineralized materials and false signals due to loop movement
Can effectively locate small metal items carried on or within a person and is substantially more sensitive than the average low cost metal detectors used at airports, so that a given metal item can be found at a greater distance from the search loop itself
Search loop and cord are waterproof, so searches in water may be up to the control box
Detects all metals
Detects intersections of rebar or mesh
Signals audio and visual indications of nearby metal
Rugged construction
Quick-tune, ready for operation in seconds as only the penetration control needs to be adjusted for most operations, allowing maximum penetration depth for metals
Accurately pinpoints steel reinforcing bars, or “rebars” in concrete
VLF (Very Low Frequency) operation
Operates on two universally available 9V batteries