Sends a message to a window or control and waits for acknowledgement.

Result := SendMessage(Msg , wParam, lParam, Control, WinTitle, WinText, ExcludeTitle, ExcludeText, Timeout)



Type: Integer

The message number to send. See the message list to determine the number.

wParam, lParam

Type: Integer or Object

The message parameters. If omitted, each parameter defaults to 0.

Each parameter must be an integer or an object with a Ptr property, such as a Buffer. For messages which require a pointer to a string, use a Buffer or the StrPtr function. If the string contained by a variable is changed by passing the variable's address to SendMessage, the variable's length must be updated afterward by calling VarSetStrCapacity(&MyVar, -1).

If AutoHotkey or the target window is 32-bit, only the parameter's low 32 bits are used; that is, values are truncated if outside the range -2147483648 to 2147483647 (-0x80000000 to 0x7FFFFFFF) for signed values, or 0 to 4294967295 (0xFFFFFFFF) for unsigned values. If AutoHotkey and the target window are both 64-bit, any integer value supported by AutoHotkey can be used.


Type: String, Integer or Object

If this parameter is omitted, the message will be sent directly to the target window rather than one of its controls. Otherwise, this parameter can be the control's ClassNN, text or HWND, or an object with a Hwnd property. For details, see The Control Parameter.

If this parameter specifies a HWND (as an integer or object), it is not required to be the HWND of a control (child window). That is, it can also be the HWND of a top-level window.


Type: String, Integer or Object

A window title or other criteria identifying the target window. See WinTitle.


Type: String

If present, this parameter must be a substring from a single text element of the target window (as revealed by the included Window Spy utility). Hidden text elements are detected if DetectHiddenText is ON.


Type: String

Windows whose titles include this value will not be considered.


Type: String

Windows whose text include this value will not be considered.


Type: Integer

The maximum number of milliseconds to wait for the target window to process the message. If omitted, it defaults to 5000 (milliseconds). If the message is not processed within this time, a TimeoutError is thrown.

Return Value

Type: Integer

This function returns the result of the message, which might sometimes be a "reply" depending on the nature of the message and its target window.

The range of possible values depends on the target window and the version of AutoHotkey that is running. When using a 32-bit version of AutoHotkey, or if the target window is 32-bit, the result is a 32-bit unsigned integer between 0 and 4294967295. When using the 64-bit version of AutoHotkey with a 64-bit window, the result is a 64-bit signed integer between -9223372036854775808 and 9223372036854775807.

If the result is intended to be a 32-bit signed integer (a value from -2147483648 to 2147483648), it can be truncated to 32-bit and converted to a signed value as follows:

MsgReply := MsgReply << 32 >> 32

This conversion may be necessary even on AutoHotkey 64-bit, because results from 32-bit windows are zero-extended. For example, a result of -1 from a 32-bit window is seen as 0xFFFFFFFF on any version of AutoHotkey, whereas a result of -1 from a 64-bit window is seen as 0xFFFFFFFF on AutoHotkey 32-bit and -1 on AutoHotkey 64-bit.

Error Handling

A TargetError is thrown if the window or control could not be found.

A TimeoutError is thrown if the message timed out.

An OSError is thrown if a message could not be sent. For example, if the target window is running at a higher integrity level than the script (i.e. it is running as admin while the script is not), messages may be blocked.


This function should be used with caution because sending a message to the wrong window (or sending an invalid message) might cause unexpected behavior or even crash the target application. This is because most applications are not designed to expect certain types of messages from external sources.

SendMessage waits for the target window to process the message, up until the timeout period expires. By contrast, PostMessage places the message in the message queue associated with the target window without waiting for acknowledgement or reply.

String parameters must be passed by address. For example:

WinWaitActive "ahk_class AutoHotkey"
SendMessage 0x000C, 0, StrPtr("New Title")  ; 0X000C is WM_SETTEXT

To send a message to all windows in the system, including those that are hidden or disabled, specify 0xFFFF for WinTitle (0xFFFF is HWND_BROADCAST). This technique should be used only for messages intended to be broadcast, such as the following example:

SendMessage 0x001A,,,, 0xFFFF  ; 0x001A is WM_SETTINGCHANGE

To have a script receive a message, use OnMessage.

See the Message Tutorial for an introduction to using this function.

Window titles and text are case sensitive. Hidden windows are not detected unless DetectHiddenWindows has been turned on.

PostMessage, Message List, Message Tutorial, OnMessage, Automating Winamp, DllCall, ControlSend, MenuSelect


Turns off the monitor via hotkey. In the SendMessage line, replace the number 2 with -1 to turn the monitor on or replace it with 1 to activate the monitor's low-power mode.

#o::  ; Win+O hotkey
    Sleep 1000  ; Give user a chance to release keys (in case their release would wake up the monitor again).
    ; Turn Monitor Off:
    SendMessage 0x0112, 0xF170, 2,, "Program Manager"  ; 0x0112 is WM_SYSCOMMAND, 0xF170 is SC_MONITORPOWER.

Starts the user's chosen screen saver.

SendMessage 0x0112, 0xF140, 0,, "Program Manager"  ; 0x0112 is WM_SYSCOMMAND, and 0xF140 is SC_SCREENSAVE.

Scrolls up by one line (for a control that has a vertical scroll bar).

SendMessage 0x0115, 0, 0, ControlGetFocus("A")

Scrolls down by one line (for a control that has a vertical scroll bar).

SendMessage 0x0115, 1, 0, ControlGetFocus("A")

Asks Winamp which track number is currently active (see Automating Winamp for more information).

SetTitleMatchMode 2
track := SendMessage(0x0400, 0, 120,, "- Winamp")
track++  ; Winamp's count starts at 0, so adjust by 1.
MsgBox "Track #" track " is active or playing."

Finds the process ID of an AHK script (an alternative to WinGetPID).

SetTitleMatchMode 2
DetectHiddenWindows true
pid := SendMessage(0x0044, 0x405, 0, , "SomeOtherScript.ahk - AutoHotkey v")
MsgBox pid " is the process id."