procedure TForm1.FormDeactivate(Sender: TObject);
begin
  ReleaseCapture;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if GetCapture = 0 then
    SetCapture(Form1.Handle);
  if PtInRect(Rect(Form1.Left,
    Form1.Top,
    Form1.Left + Form1.Width,
    Form1.Top + Form1.Height),
    ClientToScreen(Point(x, y))) then
    Form1.Caption := 'Мышка на форме'
  else
    Form1.Caption := 'Мышка за пределами формы';
end;