Do away with your PK Rings! This is an electronic accessory that you could work into any effect where the use of magnets are employed. The detection range is dependant upon the size of magnet you are using. It is a vibration unit. It can be worn comfortably under your clothing.
A ball is given to a spectator(s), they can freely choose one of them to hold the ball on hand, magician just feel / touch spectator(s) hand then can find out which one hold the ball. It can be perform anytime anywhere and repeat performing without reset, very very cool mentalism magic!