They don't know what they are. I don't know whether the spring insides are metal, and so they just see coils of metal in the scanner or what. But, when they're closed, if you don't know what they are you'd never guess what they are. They just look like disks.

They ask what they are, and I have to tell them how to open them. (Because obviously I'm traveling with them closed, as is the space-saving intention.)