Bulk iron is ferromagnetic, but many iron-containing molecules are not. Haemoglobin is not ferromagnetic. http://www.revisemri.com/blog/2006/mri-blood-iron-attraction...

I'd heard that severe haemochromatosis could trigger a metal detector. Is that just an urban legend?

It is paramagnetic, depending on oxygenation, so maybe.

Not necessarily. Iron oxide is somewhat ferromagnetic but iron chloride is paramagnetic. So just having some iron atoms in something isn't enough to make it ferromagnetic.

http://www.thenakedscientists.com/HTML/questions/question/28...

Indeed, even stainless steel isn't necessarily ferromagnetic, even though it's mostly iron.

Even very hot iron is not magnetic. ( http://en.wikipedia.org/wiki/Curie_temperature )