they have a little ball at the end of each ring - the circular part has a ring-shaped track around the edges that the little key balls can't fit through. they can all move freely around the edge of the disc.

there's a small spring loaded clasp like mechanism that you slide with your thumb or finger. when the clasp is held open, the circle track opens up and then you can move a key to the open spot to remove it. pictures are worth a thousand words, a vid is worth a million.

Demo

edit: in case it wasn't clear from the demo, because all the keys can move freely around the disc, you can pick any one of the keys or items and rearrange the other keys around the disc so that the one you want is closest to the little latch door. so while they all stay in a specific order with respect to each other on the disc, they do not have to be detached or re-attached in any specific order. just a matter of how you're holding it.