Turn on/off monitor - CodeProject

Introduction

The SendMessage function is useful to handle monitor states - the display is going to low power, the display is being shut off and the display is turned on.

Code explanation

While using SendMessage function, you have to set four parameters:

hWnd
Handle to the window whose window procedure will receive the message. If you don't want to bother creating a window to send the message to, you can send the message to all top level windows (HWND_BROADCAST) or you can use GetDesktopWindow function sending the message to the desktop window.
Msg
Specifies the message to be sent (WM_SYSCOMMAND).
wParam
Specifies additional message-specific information (SC_MONITORPOWER).
lParam
- 1 - the display is going to low power.
- 2 - the display is being shut off.
- -1 - the display is being turned on (undocumented value).

// Turn off monitor
Sleep(500); // Eliminate user's interaction for 500 ms
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) 2);

// Turn on monitor
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) -1);

// Low power monitor
Sleep(500); // Eliminate user's interaction for 500 ms
SendMessage(HWND_BROADCAST, WM_SYSCOMMAND, SC_MONITORPOWER, (LPARAM) 1);

License

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About the Author

Dalibor Drzik

Web Developer

Slovakia

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Re: Control your monitor by software

Member 4728804

18:12 2 Jun '08

Did u got any updates on ur query, even im having the same need, help me out if u found a solution. thanks a ton!!
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Re: Control your monitor by software

Member 4728804

22:08 2 Jun '08

WmiSetBrightness Method of the WmiMonitorBrightnessMethods Class The WmiSetBrightness method sets the display brightness of a computer monitor.
Sign In·View Thread·Permalink	2.00/5 (1 vote)

FYI

Michael Dunn

8:07 13 Jun '06

Raymond Chen just blogged[^] about how braodcasting this message is a bad idea. --Mike-- Visual C++ MVP LINKS~! Ericahist \| PimpFish \| CP SearchBar v3.0 \| C++ Forum FAQ VB > soccer
Sign In·View Thread·Permalink	5.00/5 (2 votes)

Re: FYI

Dalibor Drzik

7:29 4 Apr '07

Hmmm, obviously Raymond is right.

I wrote:

If you don't want to bother creating a window to send the message to, you can send the message to all top level windows (HWND_BROADCAST) or you can use GetDesktopWindow function sending the message to the desktop window. D'Oh! | :doh:

So it's preferable to say "always create a window and use its handle" or if you don't want to bother creating a window to send the message to then don't use this method. Roll eyes | :rolleyes:

And how to turn off harddisk?

andreasm82

1:26 11 Jun '06

Great program! I like it. And is there a similar solution to directly turn off a hard-disk? I need such a small program for testing purposes! Please help
Sign In·View Thread·Permalink	3.00/5 (3 votes)

Detect monitor changes?

Judge42

8:43 3 Apr '06

Hi,

Can you use this to detect when a screen goes into a different power mode? I would like to make an application which pauses itself when the machine is unattended for a period of time and was going to use the screen going into power-save mode. I found the SENS COM+ interface which notifies an application of a bunch of useful things. I had assumed that the screensaver notification it delivers would also tell me about the screen blanking if the energystar setting is selected, but it doesn't.

Re: Detect monitor changes?

Dalibor Drzik

3:11 24 Apr '06

WM_POWERBROADCAST
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Good Job!

John R. Shaw

16:46 16 Mar '06

I rated this as a 5 (to my surprise), because I like simple solutions to problems. I know finding the solution is not always easy, which you did. I hope some one adds this to a FAQs some where. INTP Every thing is relative...
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Re: Good Job!

Dalibor Drzik

2:08 17 Mar '06

Hi. Thank you for your encouragement. Anyway I found more complicated solutions e.g. in Windows version requirements macros or in Find and kill a process which uses the specified loaded dynamic library (.dll) articles.
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How to turn off monitor

uyencpham

10:56 16 Dec '05

I can use SendMessage or PostMessage to turn on or turn off the monitor. The problem is I have multiple VGA cards that link to multiple monitors. I just want to turn off the individual one. Can anybody help me?
Sign In·View Thread·Permalink	3.50/5 (2 votes)

Re: How to turn off monitor

Dalibor Drzik

4:05 18 Dec '05

Hi, I think this is not possible using the standard WinAPI.
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I tried using C# but it wont work , where i am missing

Lalit N Dubey

1:38 16 Aug '05

Hi,
This is nice exe and working perfectly.But i tried using C# and found its not workking , i think i am missing somewhere Frown | :(

plz guid me .

I used the code as folows.

The name space I used is :
using System.Runtime.InteropServices;

Now I declared the varrbale

const int MONITOR_ON = -1;
const int MONITOR_OFF = 2;
const int WM_SYSCOMMAND = 0x0112;
const int SC_MONITORPOWER = 0xF170;
const UInt32 ES_CONTINUOUS = 0x80000000;

//declared methods

[DllImport("user32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
static extern bool PostMessage(IntPtr hWnd, UInt32 Msg, int wParam, int lParam);

[DllImport("user32.dll")]
static extern IntPtr GetDesktopWindow();

// written following code in page load.

System.Threading.Thread.Sleep(2000);
PostMessage(GetDesktopWindow(), WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_OFF);
System.Threading.Thread.Sleep(2000);

Please help me out.

Regards,

Lalit Narayan Dubey
S/W Developer , Noida

Re: I tried using C# but it wont work , where i am missing

OMalleyW

3:12 16 Aug '05

Try this



using System.Runtime.InteropServices;

//

//inside class

[DllImport("user32.dll")]

private static extern int SendMessage(int hWnd, int hMsg, int wParam, int lParam);

//

public int WM_SYSCOMMAND	= 0x0112;

public int SC_MONITORPOWER	= 0xF170;

// I added a button for the event

private System.Windows.Forms.Button button1;

//

// On button click blank out monitor

//

private void button1_Click(object sender, System.EventArgs e)

{

int result = 0;

//

// get handle to active form

//

result = SendMessage(ActiveForm.Handle.ToInt32(), WM_SYSCOMMAND, SC_MONITORPOWER, 2);

//

}

Re: I tried using C# but it wont work , where i am missing

Lalit N Dubey

18:48 16 Aug '05

Hi,
Its really working great.thanks. I tried one thing more to have the desktop alwayas live. from control pannel setting i set turn off monitor in 1 min.
and written the code like this in button click

private void button1_Click(object sender, System.EventArgs e)
{
int result = 0;
//
// get handle to active form
//
result = SendMessage(ActiveForm.Handle.ToInt32(), WM_SYSCOMMAND, SC_MONITORPOWER, -1);
//
}

but it dont work, the monitor get power down.
What else need to change in application. please help me out here too.

Regards,

Lalit Narayan Dubey
S/W Developer,Noida

Re: I tried using C# but it wont work , where i am missing

Dalibor Drzik

2:29 18 Aug '05

Hmmm, would you like to disable monitor power off function?

Well, use this code but it's not C# code.

#include <windows.h>

 

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

 

int __stdcall WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)

{

	static TCHAR	szAppName[] = TEXT("Disabler");

	HWND			hwnd;

	MSG				msg;

	WNDCLASS		wndclass;

 

	wndclass.style			= CS_HREDRAW | CS_VREDRAW;

	wndclass.lpfnWndProc	= WndProc;

	wndclass.cbClsExtra		= 0;

	wndclass.cbWndExtra		= 0;

	wndclass.hInstance		= hInstance;

	wndclass.hIcon			= LoadIcon(NULL, IDI_APPLICATION);

	wndclass.hCursor		= LoadCursor(NULL, IDC_ARROW);

	wndclass.hbrBackground	= (HBRUSH) GetStockObject(WHITE_BRUSH);

	wndclass.lpszMenuName	= NULL;

	wndclass.lpszClassName	= szAppName;

 

	if (!RegisterClass(&wndclass)) 

	{

		MessageBox(NULL, TEXT("This program requires Windows NT!"), szAppName, MB_ICONERROR);

		return 0;

	}

 

	hwnd = CreateWindow(szAppName, TEXT("Screensaver && Monitor Power Saving are temporary disabled..."),

						WS_OVERLAPPEDWINDOW,

						150, 150,

						500, 250,

						NULL, NULL, hInstance, NULL);

	

	ShowWindow(hwnd, nCmdShow);

	UpdateWindow(hwnd);

 

	while(GetMessage(&msg, NULL, 0, 0)) 

	{

		TranslateMessage(&msg);

		DispatchMessage(&msg);

	}

 

	return ((int) msg.wParam);

}

 



LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)

{

	switch (message)

	{

		case WM_SYSCOMMAND:

 

			switch (wParam) 

			{	

				// disable screen saver and monitor power-saving mode

				case SC_SCREENSAVE:

				case SC_MONITORPOWER:

		  

					return 0;

			}

 

			break;

 

		case WM_DESTROY:

 

			PostQuitMessage(0);

			

			return 0;

	}

 

	return DefWindowProc(hwnd, message, wParam, lParam);

}

Excellent - but i need it in VB

Anonymous

5:59 4 Aug '05

Works great ... in c++ ... how do i get it to work in vb ? Stoopid SendMessage declare in vb doesnt work Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Long) As Long any ideas ? :: For all the hours you save writing user progs in vb, you spend twice as long implenting one tiny windows API call ...
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Re: Excellent - but i need it in VB

Anonymous

6:21 4 Aug '05

Oh, see it can be done in VB Smile | :)

Note the commented line that *doesnt* work ...

(Tested on Win2k sp4)

Private Declare Function SendMessageVal Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

Public Sub WakeMonitor()

'SendMessageVal &HFFFF, &H112, &HF170, -1 ' Doesnt work !&@!
SendMessageVal &HFFFF, &H112, 61808, -1

End Sub

Re: Excellent - but i need it in VB

Anonymous

14:02 4 Aug '05

Oops, that works only for the monitor off command - the monitor on command works momentarily and then monitor switches off again, unless it is immediately followed by a MsgBox() command to open a modal message box - which of course stops our app from doing what it's supposed to. Once again, vb has proved to be a complete piece of **** What now ?
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Re: Excellent - but i need it in VB

Anonymous

14:36 4 Aug '05

At last

Well, the monitor off command may not work in a vb app, but the following seems to be a workaround - it sticks a SHIFT_DOWN and a SHIFT_UP keypress sequence into the keyboard buffer. Ive only tested it on a machine with a keyboard attached so dont know if it works on keyboardless systems ...

Private Declare Sub keybd_event Lib "user32" (ByVal bVk As Byte, ByVal bScan As Byte, ByVal dwFlags As Long, ByVal dwExtraInfo As Long)

keybd_event &H1, &H45, 1, 0
keybd_event &H1, &H45, 1 + 2, 0

Re: Excellent - but i need it in VB

codephoenix

17:29 1 Oct '05

In VB &HF170 is an integer and evaluates to -3728 If you append another "&", vb knows it is a long: &HF170& = 61808 (That's why the first code didn't work.) Try using the following to turn the monitor On: SendKeys "{PRTSC}" 'simulate a keypress to wake the computer up an application will never receive that keypress, so it is completely safe (see sendkeys documentation)
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Re: Excellent - but i need it in VB

uyencpham

11:13 16 Dec '05

Public Const SC_MONITORPOWER As Long = &HF170&
Public Const MONITOR_ON = -1
Public Const MONITOR_LOW = 1
Public Const MONITOR_OFF = 2

Public Declare Function SendMessageByNum Lib "user32" Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, byval lParam As Long) As Long

Public Sub TurnOnMonitors()
SendMessageBynum GetDesktopWindow, WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_ON
End Sub

Public Sub TurnOffMonitors()
SendMessageBynum GetDesktopWindow, WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_OFF
End Sub

Public Sub DimMonitors()
SendMessageBynum GetDesktopWindow, WM_SYSCOMMAND, SC_MONITORPOWER, MONITOR_LOW
End Sub

Note: If you have more than 1 monitor, it will turn on or off all of them. I am seeking for the solution to turn on or turn off individual monitor

I had no idea...

Tom Archer

6:35 25 Jul '05

...that you could even do this. Thanks for sharing! Cheers, Tom Archer - Archer Consulting Group "So look up ahead at times to come, despair is not for us. We have a world and more to see, while this remains behind." - James N. Rowe
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Re: I had no idea...

Ted Ferenc

12:33 25 Jul '05

I thought everyone knew this! Just goes to show how a 'simple' article that to one indvidual is obvious and a waste of time, can be of great use to others. Which is one of the reasons why I like CP! "An education isn't how much you have committed to memory, or even how much you know. It's being able to differentiate between what you do know and what you don't." - Anatole France
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Re: I had no idea...

Tom Archer

13:07 25 Jul '05

Definitely. One thing I often struggle with is what to put in a book as I'm always thinking "everybody knows this". I don't honestly know if I'll ever have a need for this - hence my lack of knowledge of its existence - but it's cool to know just in case. Tom Archer - Visual C++ MVP Archer Consulting Group
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