How does UIRT wake from S3?

Hopefully my UIRT is in the post so I can begin playing early next week, however first I need to conquer Girder and powering up from S3 so I'm wondering how.
Does the UIRT wait for a predefined IR signal and in response send a 'power-up' command down the USB - or something similar? Maybe it looks for any IR - although this would cause an HTPC to be waking up far too regularly...
Any thoughts?
Cheers
Lea
Does the UIRT wait for a predefined IR signal and in response send a 'power-up' command down the USB - or something similar? Maybe it looks for any IR - although this would cause an HTPC to be waking up far too regularly...
Any thoughts?
Cheers
Lea