The wristband holds a rectangle grid of coded signals which tell the pitcher which pitch she is intended to throw. The catcher also wears a wristband with the same signals attached, so she is on the same page as to which pitch will be thrown. The pitcher must take the signal off the wristband while standing behind the pitching rubber.

The catcher looks on her wrist band for what the 3 digit code means. The catcher has to get the code, look up its meaning, then relay the pitch to the pitcher. It is uncrackable but does delay the game some... Not if the catcher and pitcher both have the wristbands.