[Korrin takes out her own, beneath the dragon's tooth necklace also in her possession, and nods.]

Understandable, but not to worry. By default, it will send messages to everyone but you can decide to refine the message's intended recipients as needed. You just touch the crystal and say their name or names.

They can be turned on and off, too. There's a twisting motion you make while saying 'on' or 'off', and while it's off, the crystal won't relay any messages immediately, but store them for later listening. You'll know when there are messages, because it will glow--like it's doing now.