The FENIX helps to contract the anal sphincter, keeping it closed unless sufficient force is voluntarily applied during trips to the bathroom. As soon as the pressure lets off, and bracelet contracts back to its original position.
The device is implanted using a single incision and the size of the bracelet is determined using a provided tool. X-rays are used to confirm the appropriate size of the implant and following the procedure to make sure the FENIX fits well.
From the FDA statement regarding the study that led to the approval: