Big league pitchers can signal electronically what they plan to throw this year.
Major League Baseball expanded use of the PitchCom device to pitchers in addition to catchers on Friday.
"Use of the PitchCom device is optional for clubs and wholly voluntary for players," MLB said in a memo to teams. "The decision of one club to not use the PitchCom device shall not preclude their opposing club from using the PitchCom device."
MLB adopted the PitchCom device last season, allowing catchers to push buttons on wristbands to call for fastballs, curves, changeups and anything else, along with the location. The pitcher heard the result on an earpiece inside his hat.
MLB will provide each team at least three transmitters, 12 receivers and two charging cases. Teams may not have more than three transmitters or 12 receivers at any time.
Up to five receivers may be used on the field by a defensive team at any time. Batters and runners can't use the device.