For the last few months, I had been plagued with an issue where my laptop would seemingly at random come out of sleep. I found no useful information in the event log, and couldn’t pin down the cause. When my laptop was in my bag, it made a nice heater – scary, and luckily I never suffered damage from it. After disabling all possible “wake on ___” settings to no avail, I finally stumbled upon the easy way to figure this out! Microsoft built in a couple of useful features into powercfg to help track this down. 

To find the last reason for wakeup, use powercfg /lastwake, examples:

C:>powercfg -lastwake
Wake History Count – 1
Wake History [0] 
  Wake Source Count – 1 
  Wake Source [0]   
    Type: Wake Timer   
    Owner: [SERVICE] DeviceHarddiskVolume3Program Files (x86)Ant.comIE add-onAntUpdaterService.exe (AntUpdaterService)

C:>powercfg -lastwake
Wake History Count – 1
Wake History [0] 
  Wake Source Count – 1  
  Wake Source [0]   
    Type: Fixed Feature   
    Power Button

To find out the next scheduled time for a wake up, use powercfg /waketimers (run as administrator):

C:WINDOWSsystem32>powercfg /waketimers
Timer set by [PROCESS] DeviceHarddiskVolume3WindowsSystem32services.exe expires at 3:33:36 AM on 2/8/2013.
  Reason: Windows will execute ‘NT TASKMicrosoftWindowsMedia Centermcupdate_scheduled’ scheduled task that requested waking the computer.

With a little investigation, I can finally figure out what has been messing with me, and conserve some of my battery life.