The Prisoner's Ring is magically attuned to a Jailer's Ring. When the wearer of a Jailer's Ring places a Prisoner's Ring on a subject, the prisoner cannot remove the ring without the use of a remove curse, limited wish, miracle, or wish spell. The wearer of the jailer's ring can also remove a linked prisoner's ring at any time.
The wearer of the Jailer's Ring is aware of any of the wearer of a linked Prisoner's Ring and allows him to mentally monitor their relative positions and general condition. He is aware of direction and distance to the wearer and any conditions affecting him: unharmed, wounded, disabled, staggered, unconscious, dying, nauseated, panicked, stunned, poisoned, diseased, confused, or the like as long as they are on the same plane of existence Additionally, all scrying on and teleporting to the wearer of the Prisoner's Ring is made easier.
More nefariously, the ring can be activated to kill the wearer at the will of the connected Jailor's Ring's wearer.
One such ring was placed on Nero's finger before being removed via digit amputation.