SendMessage/SC_MONITORPOWER won't turn monitor ON when running Windows 8

Question

I turn my monitors on and off by using the following code:

[DllImport("user32.dll")]
static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);

private const int WM_SYSCOMMAND = 0x0112;
private const int SC_MONITORPOWER = 0xF170;
private const int MonitorTurnOn = -1;
private const int MonitorShutoff = 2;

//Turn them off
SendMessage(f.Handle, WM_SYSCOMMAND, (IntPtr)SC_MONITORPOWER, (IntPtr)MonitorShutoff);

//Turn them on
SendMessage(f.Handle, WM_SYSCOMMAND, (IntPtr)SC_MONITORPOWER, (IntPtr)MonitorTurnOn);

This used to work as intended, but after installing Windows 8 (I assume this is the reason, since I see others have the same issue) turning the screen on won't work. I can still turn it off, but no matter how many times I run SendMessage() with MonitorTurnOn, I still have to move the mouse or press a key to get the monitors back on.

Any suggestions on how to make this work on Windows 8?

Solution 1

I had the same problem, the solution I found is to move the mouse :

mouse_event(MOUSEEVENTF_MOVE, 0, 1, 0, NULL);
Sleep(40);
mouse_event(MOUSEEVENTF_MOVE, 0, -1, 0, NULL);

It will wake the monitor on. Earlypearl

Solution 2

Here's Earlypearl's answer with the needed includes:

[DllImport("user32.dll")]
static extern void mouse_event(Int32 dwFlags, Int32 dx, Int32 dy, Int32 dwData, UIntPtr dwExtraInfo);

private const int MOUSEEVENTF_MOVE = 0x0001;

private void Wake(){
    mouse_event(MOUSEEVENTF_MOVE, 0, 1, 0, UIntPtr.Zero);
    Sleep(40);
    mouse_event(MOUSEEVENTF_MOVE, 0, -1, 0, UIntPtr.Zero);
}

Solution 3

I had the same idea for this issue Just Changed the dear earlypearl's solution a wee bit and tested it on windows XP, 7, 8, Server 2008 and all worked perfectly.

mouse_event(MOUSEEVENTF_MOVE, 0, 1, 0, UIntPtr.Zero);

it does not need to be called twice.

Comments

[Erlend D.]

Thank you, even though it isn't a perfect solution, it seems to work. I wasn't allowed to edit your answer to include the DllImport and constant, so I added one myself below.

[David Heffernan]

No need for any Sleep here. A single move with delta 0, 0 will suffice.

[Doin]

Though this question is tagged C#, some people might also be looking for a way to do this in a .bat file, or powershell script or from a Task Scheduler action, in which case this answer superuser.com/a/1371383 suggests a solution. In a .bat file this line will move the mouse 40 pixels right: powershell (Add-Type '[DllImport(\"user32.dll\")]^public static extern void mouse_event(uint dwFlags, int dx, int dy, uint dwData, int dwExtraInfo);' -Name user32 -PassThru)::mouse_event(1,40,0,0,0)

[Martin]

Why do you use a delay between the two movements? I tried it without and it worked fine. And why exactly 40 ms?

[Martin]

While a single move suffices to turn the monitor on, it should be undone by a movement in the other direction because the user may have positioned the cursor on a specific GUI element before and a blind click on a different position may lead to unwanted actions. This is especially true if there’s any chance the movement is triggered multiple times.