According to the search results, MLB pitchers have a six-inch rubber receiver inside their hats that communicate the pitch call with a computerized voice - either in Spanish or English - that will tell the pitcher, for instance, "fastball up" or "curveball, down and in". The receiver is part of the PitchCom technology, which is a wearable device that transmits signals from catcher to pitcher. The PitchCom technology is optional and was approved by the MLB Players Association after receiving generally positive feedback in experimental usage at the Single-A level last year and in big league camps during Spring Training this year.