Adam's Site on systems administration

Each scheduled task in Windows has the option to wake the computer out of sleep in order to run. But in order for this feature to work, there is at least one other prerequisite that has to be met, and that is to enable the “Allow Wake Timers” setting on the active power plan.

 

How would you enable wake timers automatically?

Unfortunately, there isn’t a GPO setting (that I am aware of) that will allow you to easily configure this setting.

Looking at the registry, there is a key which could be used to enable\disable wake timers, but the path depends on the power plan GUID, sleep category GUID, and the wake timer GUID.

HKLM:\SYSTEM\CurrentControlSet\Control\Power\User\PowerSchemes\(Power Plan GUID)\(Sleep Category GUID)\(Allow Wake Timer GUID)
ACSettingIndex = 0 or 1 –When plugged in.

DCSettingIndex= 0 or 1 –When running on battery.

Where a value of 1 is enable, and 0 is disable.

Because using the registry requires knowledge of these GUIDs, a more elegant solution would be to use the built-in powercfg.exe utility that is available on all modern copies of Windows. This utility has the ability to gather information from all configured power schemes, and can actually set values for the wake timer setting as well.

More information on powercfg can be found here.

Here is a PowerShell script that uses powercfg.exe to enable the “Allow Wake Timers” setting for all power schemes on a computer. It can be deployed via GPO as a logon\logoff script or by any endpoint management system.

The script is fairly short, so I’ll explain how it works.

1. The first task is to gather the information on all the power schemes configured on the computer. This is done by calling powercfg.exe /LIST, which outputs text similar to the image below.

This text is immediately piped to select-string which creates a list containing each power scheme.

$PowerSchemes = (powercfg.exe /LIST) | Select-String "power scheme guid" -List

The Allow Wake Timers GUID is gathered in a similar manner.

$AllowWakeTimersGUID = ((powercfg.exe /q) | Select-String "(Allow wake timers)").tostring().split(" ") | where {($_.length -eq 36) -and ([guid]$_)}

2. The entire Power scheme list is then passed through a for loop, where each power scheme is reduced to its GUID.

$PowerSchemeGUID = $PowerScheme.tostring().split(" ") | where {($_.length -eq 36) -and ([guid]$_)}

 

3. Finally, the arguments for powercfg.exe are constructed using the GUIDs. There are two different arguments: one for AC and the other for DC, I assume these correspond to the registry values mentioned earlier. And powercfg.exe is called with these arguments, one after another.

 

foreach ($PowerScheme in $PowerSchemes) {
   $PowerSchemeGUID = $PowerScheme.tostring().split(" ") | where {($_.length -eq 36) -and ([guid]$_)}
   foreach ($Argument in ("/SETDCVALUEINDEX $PowerSchemeGUID SUB_SLEEP $AllowWakeTimersGUID 1","/SETACVALUEINDEX $PowerSchemeGUID SUB_SLEEP $AllowWakeTimersGUID 1")) {
    Start-Process powercfg.exe -ArgumentList $Argument -Wait -Verb runas -WindowStyle Hidden}}

 

Conclusion

This script seems to work well on Windows 8.1 and Windows 7, but there are a few things to keep in mind:

First of all, you must run this script (like all scripts on this site) “as administrator”. Otherwise, you will be hit with a barrage of UAC prompts, one for each time powercfg.exe is called.

Secondly, the wake timer setting exists on a per power plan basis. Each power plan: “Balanced”, “Power Saver”, “High Performance”, etc… contains the “Allow Wake Timers” setting. The implication is that while “Allow Wake Timers” may be enabled for one power plan, it could be disabled on another at the same time. The power plan that is active while a computer is put into sleep dictates the machine’s ability to respond to wake timers.

My script enables the Allow Wake Timers setting for all power plans. This way, it doesn’t matter if a different plan becomes active any point in time, the computer will always have the ability to respond to wake timers. If having wake timers enabled for certain power plans, while also having it disabled on others is important for your needs, you will have to edit the script. An easy way to do this is to change the “power scheme guid” string from line 1 to the name of your target power plan(s), such as “Balanced”.

Finally, if you would like to disable wake timers for all power plans on a machine, change the 1’s in the script into 0’s (view line #6 below).

   foreach ($Argument in ("/SETDCVALUEINDEX $PowerSchemeGUID SUB_SLEEP $AllowWakeTimersGUID 0","/SETACVALUEINDEX $PowerSchemeGUID SUB_SLEEP $AllowWakeTimersGUID 0")) {

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Script(s) Used in This Post:

Enable Wake Timers (//adameyob.com/scripts/enable-wake-timers/)

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