OK, here is the final reasoning that I have gotten from our consultant and above posts:
1) Ideally is it to remove all jewelry unless it's plain and not removable. No exceptions.
2) From suggestive above with bandage/plaster. Not recommended as it's not very sanitary and would require to validate the use of metal detectable plaster. Because, the plaster may have a risk of falling into the product and at the same time, is the metal detector able to detect such a small piece of metal (nose piercing). If able to prove it, then bravo.
3) Apparently depending on the states law, some laws are extremely strict. For example, our Federal law (if they pass by for an inspection or so), they don't even accept plain non removable ring. The ring must be cut off. That is if that person is unlucky. (PS. I just learned that today from our consultant).
Otherwise, to make it less difficult, no tolerance.
I'm not saying that I don't know what to do... but just want to hear other people's thoughts.
And beside, employees like to PLAY with WORDS. They will try to find exceptions and a hole to bypass it.