Registering for WMI Events in PowerShell

Published December 16, 2016 by FoxDeploy


An alternate title might be ‘Running PowerShell Code ONLY when the power state changes’, because that was the very interesting task I received from my customer this week.

It was honestly too cool of a StackOverflow answer NOT to share, so here it goes, you can vote for it here if you thought it was worth-while.

If you want your code to trigger only when the System Power State changes, as described here, use this code.

Register-WMIEvent -query "Select \* From Win32\_PowerManagementEvent" \` -sourceIdentifier "Power" \` -action { #YourCodeHere } 

Now, this will trigger whenever the power state changes, whether you plug the device in, OR unplug it. So you might further want to stop and pause to ask the question:

Am I on power or not?

Fortunately we can use the WMI Class Win32_BatteryStatus to detect if we’re charging or not, so here’s the full construct that I use to ONLY run an operation when a power event changes, and then only if I’m no longer on Power.

Locking the workstation when the system is unplugged

Register-WMIEvent -query "Select * From Win32_PowerManagementEvent" `
  -sourceIdentifier "Power" `
  -action {
      if ([BOOL](Get-WmiObject -Class BatteryStatus -Namespace root\wmi).PowerOnLine ){
         #Device is plugged in now, do this action
         write-host "Power on!"
        #Device is NOT plugged in now, do this action
        write-host "Now on battery, locking..."

If you’re curious how this looks in real time

Registering for device events

It can also be useful to have your code wait for something to happen with devices, such as running an action when a device is added or removed. To do this, use this code.

#Register for power state change
#Where TargetInstance ISA 'Win32_Process'"
Register-WMIEvent -query "Select * From Win32_DeviceChangeEvent where EventType = '2'" `
-sourceIdentifier "Power" `
-action {#Do Something when a device is added
Write-host "Device added at $(Get-date)"

You might also want to do an action if a device is removed instead, so use this table to choose which event is right for you. Read more about it here.

EventType Id
ConfigurationChanged 1
Device Arrived 2
Device Removed 3
Device Docked 4

What else can I wait for?

Not only these, but you can trigger your code to execute on a variety of useful WMI Events, all of which can be seen in this image below!

ClassNameTriggers when
Win32_DeviceChangeEvent A device is installed, removed, or deleted, or the system is docked
Win32_VolumeChangeEventSomething happens to your disk drives
Win32_PowerManagementEventYour device is plugged, unplugged or docked
Win32_ComputerSystemEventSomething major happens to the system
Win32_ComputerShutdownEventThe system is shutting down!
RegistryEventAnythign happens to the registry
RegistryKeyChangeEventA reg key you specify is changed
RegistryValueChangeEventA reg value you specify is changed

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