{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}
{ Downloaded from The Coder's Knowledge Base                         }
{ http://www.netalive.org/ckb/                                       }
{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}
{ @ CKB Header Version.: 1.01                                        }
{ @ Category ID........: delphi_misc                                 }
{ @ Added to database..: 10.11.98                                    }
{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}
{ @ Title..............: Mouse hooks                                 }
{ @ Original Filename..: mousehook.txt                               }
{ @ Author.............: David Ullrich (ullrich@math.okstate.edu)    }
{ @ Description........: Building mouse hooks                        }
{ @ Tested w. Compiler.: not tested yet                              }
{ @ Submitted by.......: Unofficial Delphi Developers FAQ (uddf@gnomehome.demon.nl) }
{~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~}


library Hookdemo;

uses
  Beeper in '\DELDEMOS\HOOKDEMO\BEEPER.PAS';

exports
       SetHook index 1,
       UnHookHook index 2,
       HookProc index 3;

begin
   HookedAlready:=False;
end.

, where beeper.pas is like so:

unit Beeper;

interface

uses Wintypes,Winprocs,Messages;

function SetHook:Boolean;export;
function UnHookHook:Boolean;export;
function HookProc(Code:integer; wParam: Word; lParam: Longint): Longint;export;

var HookedAlready:Boolean;

implementation

var
   ourHook:HHook;


function SetHook:Boolean;
begin
  if HookedAlready then exit;
  ourHook:=SetWindowsHookEx(WH_MOUSE,HookProc,HInstance,0);
  HookedAlready:=True;
end;

function UnHookHook:Boolean;
begin
  UnHookWindowsHookEx(ourHook);
  HookedAlready:=False;
end;

function HookProc(Code:integer; wParam: Word; lParam: Longint): Longint;
begin
   if (wParam=WM_LBUTTONDOWN) then MessageBeep(0);
   result:=CallNextHookEx(ourHook,Code,wParam,lParam);
end;

end.




Now if you call the SetHook function from an application there's a beep everytime you press the left mouse button - this continues until you call the UnHookHook
function. In an actual application you're supposed to call CallNextHookEx immediately and do nothing else if code < 0 .