If you want your Windows PC to lock (i.e. require you to enter your password to use it) after a period of user inactivity, you can go to the screen saver setting and check "On resume, display logon screen". But what if you want the screensaver to be activated after e.g. 10 minutes, but you don't want the PC to lock until after 20 minutes? In Windows XP, you could resort to the ScreenSaverGracePeriod registry hack. However, in Windows 7 and later, the PC will be locked no later than 60 seconds after the screensaver kicks in, no matter what ScreenSaverGracePeriod value you have specified. To remedy this flaw, I whipped up IdleLock, a small utility that locks your PC after a selectable time of user inactivity.

See this blog post for more information.

For debugging purposes, IdleLock has rudimentary logging. Specify the -logfile option to enable logging, for example

idlelock -logfile c:\myfolder\mylogfile.log