Each of the NT200 buttons can have multiple functions, depending on whether you press and release, or you press and hold (for about 3 sec.)
Pairing Press to set the “source” that triggers instructions. “Source My hits” means you will only hear instructions right after you hit the ball. “Source opponent hits” means you will only hear them when your opponent hits the ball. Finally, “source both” means you will receive instructions in both situations. “Source both” is recommended if you are playing with a partner. “Source both” is only possible if you have paired the two devices with each other (see below).
Press and hold at the same time as your opponent presses the same button in order to pair the two devices with each other.