Finding reasons why your computer was automatically resumed from sleep mode

Putting your computer to sleep when not in use is a great way to save energy, still allowing you to return instantly back to work. Recent Windows versions have improved in this respect, and together with modern hardware, everything usually works smoothly.

Until you start to notice that your computer starts to automatically resume (wake) from sleep, only to stay on even after seemingly nothing happens. How do you troubleshoot these issues?

First, when Windows resumes automatically from sleep, several power-related entries are written to the system event log. You can easily view these through Computer Management under Event Viewer (in Windows 8.1 for example), but sometimes, the events tell only little useful information on the reasons why your computer was resumed from sleep.

For more detailed information, you can use a command-line tool called powercfg. This powerful (!) tool allows you to set system's power options, but also query current status and the reason for the latest resume operations. To do so, simply run the following command:

powercfg /lastwake

The results can be similar to this, if the computer had automatically resumed from sleep:

Wake History Count - 1
Wake History [0]
  Wake Source Count - 1
  Wake Source [0]
    Type: Wake Timer
    Owner: [SERVICE] \Device\HarddiskVolume2\Program Files (x86)\
TeamViewer\TeamViewer_Service.exe (TeamViewer)
    Owner Supplied Reason: generic

If instead you pressed the power button to resume/wake the computer, the output looks like this:

Wake History Count - 1
Wake History [0]
  Wake Source Count - 1
  Wake Source [0]
    Type: Fixed Feature
    Power Button

In addition to this parameter, the command contains many different command line options. Some of the commands require administrative rights. Thus, make sure to run powercfg as an administrator.

Good luck!