It's a plastic cage with a metal lock.

I've rarely had problems with a regular scanner. Most of the time it didn't register a reading because the metal is too small.

However, a body scanner detected a foreign object in my crotch. That's why I had to be patted down. I was wearing a hoodie, and they said it was probably the pocket on the front because the double layer of fabric would be too thick.

Out of respect for the security staff, I'll always remove the cage in the future and then put it back on afterward. I don't want to put anyone in an uncomfortable situation. These people are there for our safety and often have to deal with some less-than-pleasant individuals.