How Does the Office Communicator Presence Status Work?

I'm interested in finding out more about the Microsoft Office Communicator IM client, and how it determines your presence (i.e if you are at your computer or away). Can anyone point me towards a tutorial that explains this, or details of the API?

After a bit of research, it looks like the Office Communicator client makes use of a simple audit of keyboard and mouse activity to determine the presence of a user. This article discusses the Microsoft Communicator presence status, and these related questions also refer to it:

• https://superuser.com/questions/21364/how-do-i-detect-when-a-user-is-sitting-in-the-chair-in-front-of-a-computer/21380#21380
• Detecting user presence

It appears that Office Communicator makes use of the Windows API GetLastInputInfo Function. The following questions detail the options for calling this function (with and without P/Invoke):

• .NET equivalent for GetLastInputInfo?
• C# - Detect time of last user interaction with the OS