The Captive Segment and Captive Bead rings I use as lock alternatives use mechanical tension to lock the captive segment or captive bead into place on the clasp.

To open and close one of these requires a special tool and does take a little bit of practice before it becomes second nature to operate the clasp.

Ring opening pliers work opposite standard pliers where squeezing the handles closes the jaws so they grip something.  With this tool gripping the handles opens the jaws on these pliers and that's how you get the ring to release enough tension to pull out the segment or the ball.  

Here is a youtube video link that shows you how.

Ring Opening Pliers

This type of plier can also be called Bow Opening Pliers, or Circlip Pliers

Ring Opening Pliers

Once you have watched the video and are ready to practice keep in mind that you want to use minimal pressure to operate the locking ring.  If you grip too tightly you could destroy the lock by stretching out the ring.  Doing that would eliminate the tension needed to keep the ball or segment securely in place when the clasp is closed.