Close, but not quite.

Ferromagnetic materials do not all contain iron (i.e. are ferrous). Ferromagnetic materials include nickel and cobalt, as well as alloys of a variety of metals that are not ferromagnetic themselves.

The WTMD will detect ferromagnetic, ferrimagnetic (the compounds tend to be diamagnetic or paramagnetic materials mixed with ferromagnetic materials) and paramagnetic materials (overly simplified explanation: materials that behave like ferromagnets in the presense of a magnetic field and like diagmagnets in the absense of such a field).

The WTMD will not detect diamagnetic material (almost all materials on Earth are diamagnetic) and anti-ferromagnetic materials (rare susbstances whose lattice moments cancel each other out).

If you've got a piercing or an implant made out of a titanium alloy, it is likely to be diamagnetic, though some materials either a)have a net moment that makes them ferromagnetic or b)are very strongly diamagnetic. The latter may not set off the WTMD, but it has the potential of responding to a very strong magnetic field such as an MRI. (very important to declare all implants before undergoing an MRI!)

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