If your using Gtalk you can find out status option where you can set to busy or available option or you can type your own custom message in your status.

But if you are away PC, sometimes your friend doesn’t notifies your status message if he or she sends a message to you can deliver auto reply message using Gtalk Autoreply software tool.

Gtalk Auto reply is easy to handle, just download and install Gtalk Auto reply login to your Google account and setup your auto reply message. Finally save and enable auto reply button, now this software tool login to your Google account and sets auto reply message.