procedure TForm1.Button1Click(Sender: TObject);
var
  KeyState: TKeyboardState;
begin
  GetKeyboardState(KeyState);
  if (KeyState[VK_CAPITAL]=0) then
  begin
    // Simulate a "CAPS LOCK" key release
    Keybd_Event(VK_CAPITAL, 1, KEYEVENTF_EXTENDEDKEY or 0, 0);
    // Simulate a "CAPS LOCK" key press
    Keybd_Event(VK_CAPITAL, 1, KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP, 0);
  end
  else
  begin
    Keybd_Event(VK_CAPITAL, 0, KEYEVENTF_EXTENDEDKEY or 0, 0);
    Keybd_Event(VK_CAPITAL, 0, KEYEVENTF_EXTENDEDKEY or KEYEVENTF_KEYUP, 0);
  end;
end;