Play Alerts Through Alternate Audio Device

If you have multiple sound-output devices, such as a Griffin iMic and your internal speakers, then you can control where your alert sounds come from quite simply.

Step 1: Open System Preferences.

Step 2: Go to the Sound preference pane. (On laptop Macs, you can hit Option-Volume_Up to open System Preferences to the sound pane.)

Step 3: Go to the "Sound Effects" section if you did not go there by default.

Step 4: Under the list of available Sound Effects, there is an option for, "Play alerts and sound effects through:". Select your preferred sound device and you're good to go!