This is the Orb Ring used by Charlize Theron as Aeon Flux. I love props that actually do something, so that was part of my motivation for going after this one. When you turn the silver dial at the other end of the wire, the two little halves of the orb on the ring open up (or close, depending on which way you turn it).

This would have been usedi the scene where she starts dropping all the littlle ball-bearing bombs. When she holds her hand in front of the camera, this opens up, and then she starts taking out the little bombs. They 'enhanced' the shot with CGI after filming (adding the little bombs as she grabs them mainly), so it's a little difficult to see it actually opening on screen, but you can just barely make out the gap between the two halves.

(Auction listing photographs.)

Here's a screen shot of Aeon's hand as she's about to start grabbing the little bombs: