Given that Outlook runs in most offices, and given that a screensaver may user CPU, or network file copies, or virus scans, or network installs by the admin (granted, that usually happens when you're logged out), and all the myriad other things that might occur on a Windows 7 desktop in an office environment, how could I possibly know that a user is idled out, and not just reading a PDF?
Do I use a set of metrics to sample at regular intervals and use that to determine "away" or do I need to monitor some file, is there a API that should be exposed?
I can't rely on screensavers being active, or the computer entering a specific power state, and I'm not sure what is exactly off-limits, but I also don't know what's on-limits, as it were.
I think you're looking for GetLastInputInfo, which tells you how long it's been since the user hit a key on the keyboard or wiggled the mouse (or touched a touch-enabled screen?).
来源：https://stackoverflow.com/questions/15929790/how-specifically-does-one-detect-that-a-user-is-idle-on-windows-7